Tom,
Try looking at the parts diagrams on crowleymarine.com or shop.evinrued.com and see if the powerhead base gaskets look the same. I'm worried they won't, and that the drive shaft won't fit into your powerhead as well.
Your best bet would be finding a junk motor closer to your year, I'm thinking.
Sorry I can't be more helpful,
JBJ
A 25 mounted on a surfboard. Love it.
Looking at it I would have thought you were crazy but that boat handled it great.
I've seen butts at Wal Mart as wide as your boat.