HEI vs MSD comparison

Many youtubes showing the spark from various ignition controllers. That is in air (not high cylinder pressure) and doesn't always account for dwell vs rpm (less coil charge-up time. Still, the most powerful spark is surely from a single coil per plug which most/all current engines have (even 2 plugs per cyl like new Hemi). Among those, retro guys mostly retrofit GM LS coils (see megasquirt site). But, a single coil and distributor is certainly fine, and Mopar used that thru ~2002 (Magnum engines).

The coil is probably more important, so use an e-core type as did the big-three by the late 1980's. You can't do much more than fully charge-up the coil between sparks, which the GM HEI did (auto-dwell control) as did Ford (TFI) and Mopar (inside PCM) so not sure how MSD could do better. But, their namesake is "multi-spark" and perhaps there is value in that (Pertronix Ignitor III also has), but the big-three didn't think so or perhaps wouldn't pay royalties. Other advantages of MSD and Ignitor III are rev control.

If you go GM HEI, their 8-pin module is best (85-95 "small cap" distributor). Grab their cable & coil for easy plug n play. Also snip off the pickup connector. TrailBeast sells as a kit if scared of junkyards. Try both polarities for the pickup connection to your Mopar distributor since only way works correctly.