I just got a '54 235 back from being professionally rebuilt about 2 weeks ago. The guy who did it has done other 235's and he said in order to make the clearances right you have to shim them pretty tight. He said don't worry if it seems to be froze up when you are installing it; it's just the shims. Once you start it, they will seat and it will free up like normal. Sure enough, I couldn't turn it by hand and the starter had some trouble turning it over at first. Once it was started, everything was fine. Since the 1st start, the starter has spun it very nicely.
Also before starting it, find a long flat-head power screwdriver to spin the oil pump to get oil pressure. That will help lubricate the bearings and everything for the initial start.
Once you know the timing and everything is right (or at least close) and if 6 volts won't spin it, go ahead and jump the starter to 12. That will get it turning. It won't hurt the starter unless you just crank and crank and crank. Don't let it overheat. Once you get it started, it should free up and start easily on 6 volts if all your contacts are good and clean/tight!
Good luck!
Carl
