Ayuh,..... Sounds like the spindle got beat up, 'n somebody put a speedi-sleeve on it to save the spindle,.....
It also sounds like yer over greasin' it,...
Ayuh,..... Chevy starters only come in 2 flavors, straight across bolts or staggered pattern,.....
The flywheel diameter determines which you need,....
Ayuh,..... Welcome Aboard,..... If it's Complete, from the pulleys to the prop,..??.....
Yes, that's a wise swap,.....
Rip out all of everything OMC, 'n bolt in Everything from the Mercruiser,....
Ayuh,..... That is correct, but removin' the 2nd retaining bolt is most likely goin' to require removing alot more stuff than you want too,.....
That 2nd bolt is below the one you see, pointed straight up,....
Ayuh,..... Welcome Aboard,..... What vintage is the original motor,.....
Fix the fuel delivery issue, as it looks like you detonated that one to death,....