Now you're hitting me where I live. Seatle is one of the anchors of the Unlimited hydroplane racing circuit, going back to the 1950's.
A modeler from the Seattle area created some beautiful 1/48 resin kits of the boats from the classic era of late 1950s through early 70s, using the Craftmasters label. It doesn't seem that Craftmasters still has an online presence, but I'm pretty sure that he still sets up a booth at the annual IPMS Seattle Spring Show. There is a review of one of the Craftmaster hydros at http://www.internetmodeler.com/2002/may/first-looks/craftmasters_hydro.htm.
I still haven't built one, but a couple sit on my shelf of dreams. The one I have here is a 30' rounded bow version, a design that had several copies cranked out in the late 50s. It is around 7" in length and has a variety of parts and decals to make ten different boats, over the years. The decals and the color artwork are gorgeous. The instructions are of typical 1999-standard, really basic.
As I poked around on the web, it seems that Craftmasters also made some in 1/25 scale, and I imagine they are not cheap.
Most of the boats were not unique. In 1968 a design was built that had five or six nearly identical boats on the water at the same time. One of these was Miss Budweiser, and the MPC/ Testors kit could be used as a starting point for the others, if only there were decals available.
There is tons of more information about unlimted hydroplanes at the Unlimited Hydroplane Museum website.
Rick