Thanks all for your assistance; removed alternator this morning, to get easy access to the 3 mounting holes for generator. Holes were filled with corrosion, grease, and who knows what else. PB Blaster did the trick, all clean now and ready for bolts.

I'm not sure if what I have in front of me is proper mounting setup for this generator. I'll describe what I see... on either side of mounting bracket is a circular rubber piece. A round metal cap is positioned on top of both rubber pieces. Finally, there is a metal sleeve which goes through all 4 of these pieces. The total thickness of all this (as seen in photo) is about 5/8" long.

This can't be correct, cause a 3/4" length bolt would not be long enough to get a grip in the block. Perhaps I should remove the metal sleeve, along with one of the rubber pieces and it's metal cap. Or just get a longer bolt.