At my wit's end

Since you are thinking of an engine controller later, might be better to get an "8-pin HEI", which you find in 85-95 GM trucks and V-8 cars to 93. It has a 2nd connector for computer control of spark timing, which Holley Commander 950 can use, so I expect megasquirt can too. Unconnected, it works fine (runs at base "limp home" timing), with your distributor setting the advance as normal. Grab the GM e-core coil too and cable for a simple hookup, plus a tach output signal.

Re MPFI, my eventual plan for my slant is to install the 2 fuel rail from a V-6 Mopar on a slant intake. I have all the parts, just no time. I have a very light e-beam weld aluminum intake that people don't like, so it was real cheap. But don't wait for me. I would love to hear how your plans turn out.