Well, you have probably worked out that it is a marinised Chrysler V8. Popular in the 60's and 70's, maybe even later. For example Riva used them. The logo on the header might give a clue as to who marinised it, but suspect if it has Chrysler Marine on the bell housing it could be a factory product.
New hoses and alternator as well as resprayed. Just the one by-pass hose with overspray on (shame). Someone has spent a bit of time and money on it. Quite recently by the look of it.
It certainly looks in fine fettle.
What size of Lyman is this beast lurking in?
I have a Lyman catalogue from 1968, and they had lovely timber cruisers then in a range 16', 18', 19' and 22' (and bigger).
It is quite possible that they were still building your model 10 years later.