Here the list: changed plugs,wires,had timing reset,even replaced the fuel filter and air filter. So when I start the car it runs ok and starts off normal,but when I step on the gas(not hot rodding) to accelerate the car misses really bad....any ideas on what to check next?                          Rick (This thing got me going batty)

Assuming you have HEI on the 75 that only leaves the distributor cap and rotor....changed those? 

IF it still has it, I would suspect the EGR valve....

Well I will change the cap and rotor also the module ......it doesn't have a EGR valve on it,there is a factory looking cover where it goses. Rick

Take the rotor off, and flip it over. If you see anything that looks like lightning bolts, or any discoloration, the rotor is bad. The spark from the center contact of the coil will try to find the first ground it can, and in most cases, the closest ground is the two screws that hold the rotor on. So the spark will actually jump to the screws, instead of going down the plug wires to the plugs.
A cap and rotor will certainly help, but if you see the evidence of spark jumping on the bottom of the rotor, I would suggest you also change the coil while you're at it.

When you say that the car misses when you accelerate, do you mean the engine continues to run rough with the accelerator in a given position, or that the car "stumbles" when you step on it?  If it stumbles, then it is probably the carburetor that is the problem.  If is actually continues to miss at cruising speed, then it is another electrical problem that you haven't found yet.  I know of several fixes for the carburetor, if it is a stumbling problem.