My chevelle is sporting a shiny new summit HEI because the guy whom looked at it was prejudice against accel. It didn't fix the trouble, because the accel dizzy was just fine.

With all the symptoms you are saying, my knee jerk reaction is to pull it and inspect it to the last nut and bolt. That truck has enough room for two motors in there, pulling it is a snap.

Realistically, if you wanted to rebuild it, you would already have it out, so look at what you know already: the previous owner said to build the carb, and the old oil smelled like gas, so start there.

While the carb is being built, confirm tdc compression stroke, and make yourself a new mark on the harmonic balancer. I'd also say to pull the balancer, and inspect it, try to determine if it has spun. Maybe even confirm the block number and order a new one that you know will work.

Check under the dizzy cap for corrosion or cracks, etc. With it running, pull each wire at the plug, and look for the spark. You can even use an old plug, ground it on the block. Careful, HEI stands for high energy, and kick out 30,000 volts, and it smarts.

Keep up posted.