You could be dealing with a little rust on the cylinder walls from condensation. Some valves had to be at least partly one. It will likely be OK it you take it slow and easy. Thats where the MMO comes in with all the spark plugs removed. Work it back and forth and let the rings spread the oil and scrape the walls a little at a time.. There may be rust above and below the rings on the cylinder wall. If it's more than a light rusting it will need more attention.
There could be some stick valves and lifters too. If the engine is '56 or later it may be a 12v system. When they changed to 12v they also changed the flywheel and the ring gear won't work with a 6v starter. Although a 6v starter will work with 12v so when the engine was installed the old flywheel may have been used. I Can not remember when Chevy went from 4 to 6 bolts, about the time of the voltage change I think.
