TOPIC: 78 Tri Sonic SST 2+2

I'm new here and hoping someone can help me out or point me in the right direction. The hull and the interior are in great shape my problem is the guy that I got it from was swapping engines with a mercruiser 3.0 and an alpha One outdrive. I'm looking for a source of information of what was originally in the boat and any schematics. I don't feel the 3.0 will fit and would like to go back to original.
Any help would be greatly appreciated.