Saving Old Seagulls

1971 Forty Featherweight in running condition.
Details and photo at http://southcoast.craigslist.org/boa/401369747.html

Everything, including its age, the fact that my father used it on his dinghy, and is light enough lift to the stern rail for passage, seem to point to that model. Oh, and I'll have that gearbox cap seen to right away! Thank you both for your help.

Thanks, @rie. The date would fit. But I can't see enough difference between the first and last characters to read one as an 'I' and the other as a '1'. I wonder of anyone else has seen engine numbers with confusing 'I's, or '1's, or '5's and 'S'es, for that matter?

I've just read John's comments on the site about scarcity of 'F' engine codes. I've just turned up another one (photo - 400K) on Cape Cod in Massachusetts, that had belonged to my father. The engine code on the block looks like this:
F
I490DI

or see this photo (200K) of the number.

According to ...