I do want to give the Hei another go as well but I think aftermark 4 pins must be the way to go since you can get msd units or pertronix with great support.
Ive had great luck with pertronix HV 65k volt coils mounted off the engine.
coils-
https://www.amazon.com/gp/product/B000J ... em_1p_5_ti
pertronix hei coil 50k volt low resistance.
out of six amazon reviews half of the reviews are five start and the three others had issues after a month.
https://www.amazon.com/MSD-8225-HEI-Ign ... CSPGDPV869
this mSd coil has better reviews
Modules 4 pin:
https://www.amazon.com/gp/product/B0035 ... em_1p_1_ti
seems to have excellent reviews on summit.....digital rev limit control + multiple spark. (sounds ages above a used gm 4 pin an I cant say im a firm believer in the ac delco unit.
Or msd has a 4 pin module as well.
I believe with their live tech support and product backing its my next viable solution So tomorrow I plan to give mSd and pertronix a call but I wouldnt totally count out accel either.
see what one you feel comfortable with. Im leaning toward the gm 4 pin ignitor 3 and a pertronix coil hopefully the hi voltage or what ever they recommend.
they duraspark is kind of a big flimsy multi piece unit so the cap and rotor plus cap mount can all have algnment problems an are ages of an old system. probably the best option we have though. I honestly like the non gm in distributor mounted module as that garantees a quality hall pick up and Ive never had any problems with those modules in over ten years experience with them. Plus if you use the right special order size resitor they do work with the 65k volt hi voltage military grade pertronix HV coil series....those are the best coils hands down.
https://www.amazon.com/PerTronix-1261-I ... B000N2WAMQ
again the well know pertronix ignitor for the stock distributor which i feel is a tighter unit and in a better designed distributor one piece and the caps are actually quality on those. and excellent reviews much more 5 star reviews then any other ignition module for this engine and really all one of the inlines will ever need unless running power adders. and again the best and newest guarantied hall sensor vs duraspark used units or china modules they usually dont read proper voltage or resistance values after proper testing.
PerTronix's Ignitor® solid-state ignition systems deliver more energy with greater timing accuracy. The secret lies in the trigger magnets, which spin with the rotor and operate a switching module that requires no external control box. The systems are immune to heat, oil, and debris and install in about 15 minutes with only two wires to connect. They come with a switching module, hardware, and instructions. They're an ideal choice for collector car restoration because they fit entirely under the distributor cap.
https://www.amazon.com/PerTronix-91261- ... B001GQQT4I
THis is the ignitor 2 for the ford load o matic type early model distributor.
I would imgine this is what you want for anything above a stock small log inline six. any performance mods probably go with this.
(106 reviews on summit of the ignitor 2 and 4.5 star adverage.
Not ones to leave well enough alone, the people at PerTronix set out to better their highly successful Ignitor® ignition conversion systems. These new Ignitor II® conversion systems have all of the same quality features as the original Ignitor®, plus a powerful microprocessor controller to deliver three to five times more available energy between 3,000 and 5,000 rpm. They're an ideal choice for collector car restoration because they fit entirely under the distributor cap.
If they had a ignitor 3 for the early inline six ford that would be great so I do like the fact the pertronix HEI flame thrower 3 is multi spark and rev control limiter is probably key.
Im leaning toward going back to the igniter 2 and the High voltage pertronix coil with proper resistor.