If, as I read this, the 6 V won't start it and it is seeming to bind or drag, then my advise is to "STOP!!!" and tear the engine down and find the problem. Could be bearings, wrong or broken rings, not timed correctly or even wrong parts in the wrong engine. Suffice to say- Something is Wrong!!-. These engines will turn over and start very easy if assembled correctly. You don't need to use twelve volts or push/pull start them. Even Master Mechanics can make errors, but don't make the error of "forcing" the engine to run.
Oly in Oregon
Rest in Peace1945 GMC COE Victory Truck
1953 Willys CJ3B
1955 Chevy 1st series 3/4-ton
1958 WIFE Last series
Never say "Whoa" in a mud hole