I dont know if this will help but I recently got my 1940 GMC running after 40+ years.
I was having same issues as you; fuel in manifold, what appeared to be good spark, but no go.
I would fill the float with fresh fuel, leave off the fuel line so old fuel/junk didn't get in, (she may only run for 10-15 seconds but baby steps) carby cleaned out, but still no luck. Used a 12 volt battery and coil, no luck. My mech mate came over and had her running in 5 minutes; what he did was; while I cranked her over he held hand over carby to check suction (not precise but we had suction), he then checked spark as the points were a bit crap so he pretty much just checked they were sparking with screwdriver and gave them a few sraps to get good connection.
Then he had some 'shellite'??? or similar sounding stuff? alcohol type cleaner? (I used a bit of 'start ya bastard'later to get her going again on a later date but now she starts freely) anyway he sprayed a squirt of that down carby and I kid you not she just fired to life. And this was with me trying for days and him not really changing anything other than that spray. We also used th old original spark plugs...just sandblasted ends a little.
I also did the oil down cylinder thing a few weeks ago but still no go, until my mech sprayed that stuff in carby! LOL
