flywheel ring gear and bendix

[rer_239]

1. looks like there are two different starters (1/2 & 5/8 shaft) and two different ring gears. i'm trying to piece together an engine, how do i know if i have a matched set? i've got my spare engine on a stand and the starter engages the flywheel and rotates the engine okay so the gears seem to mesh, but the starter gear doesn't disengage the flywheel, don't know if there is a problem with the bendix or if its a problem with the ring gear and starter gear. any ideas?
thanks
dick