The 6v starter will be OK as long as you take the 6v flywheel with the bellhousing (clutch housing).

"Is there a gasket that should have been there? It must have been apart before because there was blue sealant there, but no gasket. "

Are you asking about gaskets between the transmission and the bell-housing, the bell-housing and the block, and/or, between the halves of the u-joint housing?