The 4 pin module and 7 pin module will fit in the same holes. (Top two modules in the pic below)

7 Pin Module is used with a Large Cap HEI that has the ignition coil in the cap.

8 Pin Module is...

The 8 pin HEI module can be mounted outside the distributor. Using the Ford type pickup coil can save space under the distributor cap. The pictures show the 4 pin HEI module, which is similar in...

I have experience doing EFI conversions and tuning. What I would do might not be an easy or low cost option for you?

I'm not familiar enough with the GMC 302 six cylinder, so I would first need...