Fuel gauge issues?

Wonderful. Just bend the two copper strips so the contacts sit roughly 1/16" closer to the sensing element. Don't go too much more than that as the added pressure might cause the piece to unsnap on its own. Too much pressure can also cause the contacts to wear away the resistive sensing material.

You'd have to ask a mechanic at a Toyota dealership as to what uses the same part. My only reference is the Rock Auto site where I look up part numbers. They don't list just the sending unit, just the entire pump and housing. If you have a donor car in mind, you can look up that one and see if it uses the same housing. If it does, the sending unit should be the same. If the pump number is different, it could still have the same sending unit on it. I can't tell that by their photos because even if two look the same, they might have different resistance values, different mounting clips, or be mounted at a different angle.

I did find a part number on AllData, our online service manual provider. With that number, you might consider visiting a salvage yard to look in their "Hollander Interchange Guides". Those are large books where you look up the part for your year and model, then it gets assigned a code number. You look that code number up in the back of the book and it will list every vehicle model and year that could have used that part. That can give you a wider range of vehicles to dig through, and it can verify a car in the yard is worth pulling the part from.

I also found some updated information as for the models that use this part. An older version was 8332004020. You have a newer version, 8332004021. This one was used from 2005 - 2013. There's a still newer replacement, number 8332004031 that is a replacement for 2005 - 2016 models. New, or "superseded" part numbers mean a significant change was made. That could be anywhere from a total redesign or a different supplier, to a slight change to improve reliability or to address some other issue. No other models are listed as using this part, but it can explain why you see sending units that look different but are both listed for your model. In all cases it doesn't matter which engine you have.

I can't find the resistance value of the sending unit. Three-wire sensors, like throttle position sensors, are not critical, but two-wire sensors have to be precise to read correctly, so the place to start with a sensor from a different model is with the resistance test between the two wires. Even if that is the same, that doesn't guarantee the change in resistance will be linear, or the same as the old one. For example, if the shape of the tank is such that there's more gallons in the top half than in the bottom half, the wrong sending unit could show you still have half a tank when really you're down to the last few gallons. My mother had a vehicle that read "full" until about half the tank was used up, then the gauge quickly went to empty on the last half of the fuel. We figured out that was "the nature of the beast", and the same model did that over a three-year period. When she needed a new fuel pump, we put in the entire housing assembly with the new pump and sending unit, and the fuel gauge read the same way. That's what I mean by "non-linear". To say that a different way, the gauge goes down faster or slower than the fuel is used up.

For splicing wires, I never trust any splice that doesn't involve soldering. I really dislike crimp-style butt connectors because they don't guarantee a solid joint and they don't seal out moisture. Obviously, these wires and exposed connections survive just fine in a gas tank environment, but I still would only trust splicing wires by soldering them. While logic dictates the joint doesn't need to be sealed, I would still feel better covering it with moisture-proof hear-shrink tubing.

Gauges from the 1960s through some of the '80s were thermal gauges that used a heating element. Chrysler and Ford used those because temperature changes in that heating element took a long time to affect the gauge reading. That meant sloshing levels in the gas tank had no effect. GM used the more common electromagnetic gauges. With those, the pointers would bounce wildly all over as you drove, so they had to add an "anti-slosh" module to the back side of the instrument cluster. Today all vehicles use computer circuitry to run the gauges. Built into that circuitry is a means of smoothing out the wild pulsations from sensor readings so the gauge needles remain steady. As a result, a rapid change in where you put the float arm translates into a slowly moving gauge. On many cars, if you leave the ignition switch on while filling the gas tank, you'll reach a full tank while the gauge reading is still down near a quarter or half tank. It can take a minute or two to catch up.

I'm not sure what you're doing with the plug. Do you have to remove terminals to install the new assembly? If so, there are special tools to release the tiny locking tabs on each terminal. You might be able to do that with a stretched-out paper clip or a thin pick.

From what I can see in your first photo, it looks like there's a small plastic finger just above the metal terminal, that has to be lifted up, then the terminal is pulled out by the wire. A small pick works well for that style. Often there's a small barb on the metal terminal that has to be pressed down, then the terminal is pulled out.

Epoxy should hold up to gasoline.

The gauge is in the instrument cluster / dash. You aren't working up there, are you? Your photos are of the sending unit, or sensor. Normally, if the terminals in the connector don't match, it's the wrong sending unit. It is also possible they used the same sensor on multiple models, but with different connectors. In that case it is acceptable to switch wires or connectors.

If you just need matching terminals, there's a number of sources to consider. Start by looking at the universal terminals at any auto parts store or hardware store. Next, if you don't mind rummaging through a lot of vehicles, look in a pick-your-own-parts salvage yard. "Pull-A-Part" is one chain I'm very familiar with. Their yards are very clean and well-organized. There's a lot more like them all over the country. You will need to remove the terminals from the connector bodies. Take enough wire with each one so you can splice and solder them.

You can also check at some new-car dealership parts departments. GM and Chrysler, for example, have large kits with every style of terminal used in their vehicles. I would assume all other manufacturers have something similar. The Toyota dealer might even have the right connector. Auto parts stores also have multiple very large books that show the connectors that are available for almost every application, but be warned, they tend to be horribly expensive.

If you have to poke in each terminal individually, consider using nylon zip ties so they can't vibrate out.

They make a piece of clear heat-shrink tubing that has a ring of solder inside, but you have to buy a whole pack of them. That's why I prefer to twist the wires together, then solder the joint and slide a piece of heat-shrink tubing over it with hot-melt glue inside. Those seal out moisture.