It's been 25-30 years since I worked GM HEI's , my 75 Monte Carlo and 77 Nova Concours . But I mean you would run , from Pos. battery post , a FUSED (15-20A) jumper also with a 1-2 ohm (like 5+ watt rated) resistor in series directly to the PROPER connection on the HEI , the B+ battery input ,ya know - NOW crank engine ! Should start ? No ?........Aligator clips work great here.
Oh and you would have removed what wiring from car circuit was on that HEI terminal I'm telling you to jump hot-wired , to eliminate car circuit AND for safety sake
p.s. You may have to run new jumpers from coil to HEI , but ohming them disconnected will tell if this is needed too. Inductive pickup inside distributor is more challenging to diagnose , never needed to go there.