Maybe try a different distributor. I had a similar problem with a very nice, very low mileage original 235 that I put into my 53 3/4 ton. It would start and run, but just stumbled and hesitated and would not rev up. After going through all of the usual suspects (timing, carb, fuel pump, plugs/ wires, etc.), I decided to swap the distributor--bam, it ran like a champ and has ever since. I believe a worn shaft can cause the distributor to wobble and create very inconsistent timing (knowledgeable old timers can provide more details or a more accurate description of the problem).
Best wishes, and let us know when/ how you fix it!
