I respect Tim's and other ideas. Your truck must be done as you wish. You are on the right track now.
These are my suggestions/thoughts. We are committed to a diverse forum.
Seems like a band aid to get a "better" battery for a little ol' 216. It sounds like a component breakdown which pulls the battery down. I.E. cables, connections, wires and weak starter. As I said, I would have gone to 12V along time ago. Does not change any perceptible originality. Sure would turn over faster at all times....and get this, your 46 year old problem would be solved. All cables will have less heat/less drop. All cheaper than getting an Optima which will still only have 6V to give. More reserve cost more money in any battery. Reserve (on a 12V Batt) is how long it operates before falling below 10.5V......... In this case, still plenty reserve to operate a 6V starter. Again, it will solve your issue especially with the good running, quick starting motor you have.
The questions were not about how good the motor was or your ability to fiddle. They were to be able to analyze the condition. As was the pedal position tests which are easy to do. Truck in neutral, foot on pedal, board on foot start if you wish. These tests were no different than a normal start. That's moot now, your issue is probably not fuel.
