Engine was making a light ticking noise?

Hello guys. If you could only feel my frustration. But let me get to the point. My 95 Caddi Deville 4.9L was making a light ticking noise and got more noticeable and worse. I thought of it to be a lifter, but it got to a point where I couldn't deal with it anymore. You could really only hear it when acclerating. I consider myself one to take care of their cars and try to treat it the best as I can. I did some online research and finally took it in to get checked out. To my worse fear, it was diagnosed to be a bad engine and slight rod knock at its early stages. I thought it was a crack in the exhause manifold at first. Ok, I sucked it up and spent the money on a used motor at a business where they supposively do compression tests and listen for any adnormal noises. Had my mechanic install and about 3 days later he calls me with some bad news. He says the motor I bought had a bad crankshaft (main bearings were bad). I went up there to test drive and it sounded awful. Labor is non-refundable. Ouch. I took it back to the original shop where I purchased the motor and had their shop install it. Now the car is making a bad noise again, not as terrible as the 2nd motor but its very disburbing. You can hear it at acclerating but more annoying when the motor heats up. Gosh, this is breaking the bank on me because its very expensive to pay for the labor each time, although the benefit of having the motor shop guys install is they cover any labor warranty costs. Now, the ownwer is saying it might be something else and not the motor because this is very rare to have 2 bad motors in a row. I'm not sure if he's trying to wash his hands or if he is being honest. It doesn't start knocking right away when I turn on the car. Once I put it in gear and step on the pedal you start to hear tat tat tat tat, then moments after, it starts to sound deeper, like clunk clunk clunk clunk. They did not see any metal inside the motor or water. This is two different shops who installed the motor. The intial noise didn't sound so bad but because I tried to take an early step to try to fix the problem I end up with the biggest problem in my life. I've seen videos on taditional rod knocks, mine is a little deeper than the ones I've heard. It has enough oil, they even put some lucas oil treatment but it still sounds the same. :(

I'm about to pull the plug and who knows.

Any advise is appreciated, believe me.

My name is Frank.