I did a little searching and only came up with a couple Mariah jet boats listed.  One was a 21' day cruiser similar to a Spectra or a Sanger.  The couple of 18-20' jet boats I saw looked a lot like a Hornet or Liberty hull which is a very good hull design.  The main thing is to inspect it carefully for soft or rotting floors, cracks or damage that will delay you getting it done.

The other thing that concerns me is the use of a hot rod street car engine in a jet boat.  Because of the jet boat cooling system (cold fresh water) it is best to have an engines machine work set up for a jet boat application (more piston to cylinder wall clearance to start).

There is a lot of good information on this site about what to do when building an engine for a jet boat.

Welcome to the site and enjoy the ride 

I had one 1978 18 foot had a dominator pump droop c impellor,it porpused real bad at higher speeds so I put trim tabs and all that went away and gps at 88 with two people.It was a good ol boat.