The distributors interchange in the engine, and of course the caps were different. I adapted first the GM HEI module, mounting it on the fender well on a heat sink, used it for a while in two different cars, then changed over to a TFI Ford. It by far was the simplest, in that the timing was already fixed (no centrifugal advance, so I didn't have to mechanically lock it out), and the wiring was even simpler than the HEI.
I prefer eliminating the advance, and have had no problems with engine life, or starting problems. Idle is acceptable, and the KISS method is intact.
Incidentally, don't be mislead by claims of performance problems at high RPM with the HEI...the references are ALL to the V8 application. As you know, 5000 RPM on a V8 is the same as 10,000 RPM on a 4 cylinder, and we're not going to have a problem with that!!
Both are cheap, easy to locate for replacement, and there is no discerable difference in performance. I stayed away from the MSD units because the claims for multi spark output was at lower rpm, and my concern was at the upper range of engine performance. KISS.
Good racing.
Bill