Can't figure what would be causing the drag in the engine. Since you said you didn't bother the lower end, assume all rods and mains were left as is? You didn't mix the rods around or interchange rod caps?
Is it the engine dragging (bottom end) or compression it may have now? If you remove the spark plugs does it turn easier? Usually a 6 volt system doesn't turn the engine over as fast as 12 volt does. The rope seals might cause some drag, but shouldn't be enough to keep it from starting I wouldn't think.
John
