I'll try and provide a little background first about the car.
1992 RS, I believe it was originally a V6 700r4 car. The previous owner put in a 383 GM crate engine, and there is still a 700r4 in the car and I am pretty sure it is the original. When I bought the car the only gauges that sort of worked were the middle ones (Voltage, Oil Pressure, Coolant Temp, and Gas). There is also an after market tach mounted to the dash which also didn't work when I bought the car. I found that the tach output from the distributor was just unplugged, so I plugged it back in and it started working, although I don't think it is accurate.

My theory is that when they did the motor swap, they never bothered to go through the trouble of hooking the speedometer or the original tach back up, but as far as I understand, I don't think the engine has anything to do with the speedo, but I can't find clear cut answers as to where I should start diagnosing.

Also, I am not sure how to go about getting the tach back either. I know that you have to do some resistor calibrating if you go from a V6 to a V8, but it is as simple as splicing the tach like from the distributor back into the tach input for the gauge cluster and swapping the resistor?

Any help, advice or ideas on where to start would be great!