lets check a few things..
since i am half a planet away.. its hard to come over..
lets check the power to the ignition system.. with a test light.. i am expecting you have a HEI ignition system.. probably a remote coil small cap type.. the power to the coil.. the pink or red wire.. probe it while somebody slowly turns the key from OFF to ON, to Cranking.. back to ON.. then slowly OFF..
there is an issue with ignition switches used with GM points cars.. the IGN1 circuit opens when the key is in the cranking position .. this is because while cranking the ignition power comes from the R terminal on the starter solenoid..
with electronic ignition.. you will want the results to be bright. bright bright..
if you still had a point type ignition it would be medium, bright, medium. as the resistor is bypassed in the cranking position.
do you have some kind of scan tool... that will display live data stream to allow you to see what the engine controls are doing..
with conventional GM fuel injection.. i like to see TPS voltage below 0.98 volts.. usually someplace between 0.35 and 0.75 volts.
i would like to see with the engine warmed up.. coolant temp over 190F/85C the IDLE AIR COUNTS (IAC) between 20 and 70 at hot idle in park. this gives the computer the ability to back the idle air control motor out to about 120 counts for a cold start.. so it will fast idle.
i know you mentioned that you have fuel pressure.. but can you do the voltage test ON, Cranking, ON.. at the fuel pump power circuit.. so you make sure that when you turn the key on.. even before the engine is cranked.. the PCM has commanded the fuel pump relay to turn on for at least 2 seconds and less than 3 usually.. to build fuel pressure prior to cranking.
i will have to dig up the installation instructions for the Ramjet 502.. see how they handle this.
i was looking around for my image of the later GM in dash ignition switch that usually gets used with electronic ignition conversions.. it did not open the ign1 contacts while cranking.. it does have a pair of terminals G1 and G2 that could be used with an additional relay.. to power up the fuel pump relay while cranking. but the PCM should handle that just fine as long as the system does not loose current.
you may also want to monitor the power to the PCM.. during another Off, On, cranking, On, then off tests..
edit... i am taking the engine came with the installation and service manual..
https://chevroletperformanceparts.com/p/service-manual-ram-jet-502-2
i see your post that if you touch the throttle it will never start.. touching the throttle will usually cause the engine to flood.. only holding the throttle more than half way open without pumping will clear the flood and turn off the injectors to allow it to start..
fuel injected motors don't need to touch the throttle to get them to start.. if the idle speed and Throttle position sensor / idle air control are within specs..
this is a marine version and probably slightly different than what you have.. but the fuel injection system will have the same diagnosics..
http://www.pirate4x4.com/tech/billavista/MEFI/MEFI 4 & 4B DIAGNOSTIC MANUAL (L510005P).pdf
looks like the TPS voltage should be exactly 0.60 volts with the throttle closed..