There are two different pilot bushings. If the engine was originally equipped with a Powerglide there is a special diameter bushing that converts it for use with a standard transmission. Be sure the starter and the flywheel match- - - -the 56 would have been equipped with a 12 volt starter, and the 216 would have used a 6 volt unit. There is a gear tooth mismatch between 6 and 12 volt starters and flywheels, although the 6 volt starter works OK on 12 volts. Just be sure the starter and flywheel come from the same vintage vehicle. Runout isn't usually an issue except where the fit between a Hydramatic trans and an engine block not originally mated to a hydramatic is involved.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!