Your boat is quite valuable and should receive well considered care and restoration. Be very circumspect in consideration of advice given on this venue. The audience here is almost entirely amateur. There is a handful of professionals that wander through. Now, some of the amateurs here have skills that match or exceed professional levels. Sadly however, these are far exceeded by the number of folks with limited knowledge. I know of NO professional speedboat restorers here with the exception of me. No brag, just the truth. And a warning to consider WBF advice very carefully.
Some points:
Join the Antique and Classic Boat Society. Name notwithstanding, it is a club for classic speedboats. This is the website
www.acbs.org. Here is the
closest chapter to you, I believe. They publish a directory with listings of boats owned; with this you will be able to find a sister ship and its owner.
Put in a modern engine. Original engines have their appeal certainly. However, vintage marine engine mechanics are few and far between. Almost certainly a modern engine will fit.
Almost certainly your boat's sides were varnished.
It would be worth the investment to get a professional speedboat restorer to look at your boat. I can't say that I have much experience in this model, but there are restorers are out there that do.