Bolt removal - bellhousing to transom
 

I see from old threads these things have a tendency to rust/corrode to a sleeve in the transom plate. So if I can't break these loose, and confirm I haven't broken anything where the nut is captured underneath, then that's what I'm facing? So Plan B would be trying to separate the bellhousing from the block?

Volvo uses studs in this application, I think I'd put it back together that way, if there's room.

Put a hoist on the engine and lift the engine weight off the transom assembly. Then try to back the bolts out.