1989 Ford F-250 efi 460 motor runs rough / misfire

Is the place you mounted the ground on the block cleane?
Where on the block is it?

When engineers desgin a vehichle they spend a lot of time making grounding more of a prioity than you think.
Signal to noise ratios can affect, stereos/radios, distributors/coil packs, charging systems, etc.

When you ground out a vehicle, there is a minimum amount of grounds needed to avoid things like, "backfeeding". This is where a ground is not as conductive enough as compared to a ground in the dash somewhere. The dash becomes the path of least resisitanane and then malfunctions can occurr in the isplay. This can happen in the, computer, fuel management systems, PCUs, etc.
When the minimum grounds are layed out, which are gerally a, "balamced circle", then some people even go further and add more grounds. Some become redunddant, but that never hurs.

So, you might have moved the ground into an area where it creates electromagnetic interfenerence with some component and it is affecting the siganl.

You can move the ground back or replace it on its original path and see what heppens.

Try to find points that replicate the gound. Such as, if the ground was originally on the exhaust manifold, move it to the manifold connection where the manifold first connects to the exhaust.
Keep in mind you might have to play with this as parts such as the exhaust manifold to the head may have a lot of resistance depndine on the type of gasket material. Even if it is a meatal gasket, it still will have some resistance.
So, if you mount the cable to the manifold collector, mount it on the top of connecter and try to make it touch the exhaust manifold.
Check the cable for resistance. Depending on the gauge you will have a corresponding Ohms per foot value. 1AWG is 126.4 Ohms per foot. it may be less depending on quality of cable and you have to add a few Ohms for cable ends. check resistance of cable to make sure it did not get internally frayed or the connections are bad. Visual inspection can take care of this in most cases, but to be sure you need to performa an Ohm per foot test with a multi-meter to make sure cable is good.
I you want to move the ground to the block, keep it as close to the exhasut manifold as possible.
If all else fails you can get power distribution blocks for battery posts, usually used for stereos amps, etc., which have a 1 AWG connection as well as a few other options depending on what you get. The negative battery post is the best ground there is. If you still have a problem, there is another issue that was excacerbated by moving the ground cable.
You can also get Grounding Kits which attach to the negative battery post and provide a good ground source so back-feeding does not occurr.

Here is a link to a grounding kit, the price is not bad either.

http://www.maperformance.com/nrg-grounding-wire-system.html

Here is another grounding cable system. It has a diagram of suggested ground mounting points in the engine compartment;

http://www.racinglab.com/whishygrsy.html

You can never have to many grounds. make sure ground mount points are free of paint and are clean and rust free.

Just in case it is a coincidence, here is a list of issues that cause cause rough idle, stalling and misfires;
Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Crankshaft position sensor
Knock sensor
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking or defective fuel pump.
False air leakage.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

You can also price out grounding kits by going to a car stereo shop or a Best Buy and getting an amplifier installation kit. It has ! AWG wire, sometimes bigger, high quality connectors and you have the freedom to make cables to the length you need. The cables and connectors also have less resistance per foot as they are higher quality than standard copper cable.

To reset the computer simply dis-connect the negative cable for at least 30 seconds.

If you still have problems, let me know where the other end of the ground cable goes. Also try mounting cable back to its original mounting point to see if problem goes away.

Let me know if you need anything else.

I forgot the most important point. The fact that it is the negative battery cable makes it different.
You will really have to stay close to the original mounting point and don't make a cable that is any longer or uses a smaller gauge wire than the original cable.
The only other place you might mount it is to the frame, if you can reach it.
I meant to make that my first comment before I explained grounding issues and general ideas for grounding points and systems.
It is very important that the negative battery cable have a very good ground mounting point.
I do not understand why it would have an issue being mounted on block. That is why I asked where is it mounted on block?
Either the block or the frame are generally the most common mounting points.