Any particular reason why you want to build a 1980s style craft?

If no-one has told you already, that craft is neither good for racing or cruising so you'll be stuck with operating in a private field.
The RD250LC was OK in it's day but is so outdated that it's a museum piece.

You'd be far better off getting a decent cruising hull such as an Osprey or Flying Fish and fitting it out with a Briggs and Stratton or a Kohler. This may cost you a little more but at least you'd end up with something you can actually use.

If you were building a kit car you wouldn't build a Model T Ford eh?