Thanks Dave for all your input.
great suggestions, I would have never thought of a folder. Im less of a planner than you ,Im more of a jump right in kind of guy. I will say I have been thinking of this boat for ages, so I knew what I was getting into. and it seems small compared to the Fred Murphy I was doing. and easier too at least the hull.
TBH , I was torn about doing a jetboat because I dont want to negatively affect wildlife, and fish habitat, so I will be very conscious of this fact when running rivers. In the end, the "fun" factor took hold of me, and I broke down. IM pretty determined. I also want to use the boat to access a part of the French river, that is unnavigable other than for canoeists who must portage(pronounced here as por-taage) and put a small float home there, as a summer residence. I did that once before on a similar river but closer to a small town. This time i want more seclusion.
I know I want the boat to be able to run up the rapids here, on small rivers, tributaries, outlets etc. on Georgian bay. lake Huron etc.
also to do short runs to the North Channel Islands(if you havent been , its amazing!!!) considered by many to be the top summer cruising spot in the world.
I think your from Michigan? So its similar to the same geography. except the French/key rivers, and the Rivers of the North Shore, are wonders of navigation, there is also the infamous Ottawa river, with its amazing class 3 rapids.
That alone offer some of the best jet boating in the world. except, no one does it. Part of it is that there are dams that impeded the process, so on certain rivers you can only go for a couple days in a jet boat. I am looking at expedition jet boating across north America. Maybe out West in BC or Alberta.
The reason I chose core, is the weight savings. Aluminum is much heavier than wood. And wood will not serve me on rivers.
If I can pull this off, it allows for more space and storage to bring gear. The bigger engine is a MUST for these reasons.
I did a cost benefit of AL, over core. I called up Composites canada(better than Noahs and far more friendly and efficient)
and asked them to price out what i needed and core came to under 1000.00. for the whole boat inside and out.
On the other hand a welder(i dont have one) the gun, and the Aluminum(that alone was going to be well over 1000.00 cdn), made the choice easy. I will pick up the book by Glen-l Witt on inboard engine installation, even though it is a bit outdated. My Main concern is going to be matching a pump, and wiring. Im sure its straightforward but Ive never really worked on a gas marine engine, and never have done wiring. I did think of buying the pump/engine first. But I did that with my tugboat build and it failed...soooo..
I can always adjust the transom, and not glass it in, but I think most are plumb transoms anyway. Does your transom need any "cant" in st the stern to allow for your pump? also how will you install your grate for the intake?
The Subaru engine is 899.00. I will need to marinize it, so. not sure the costs of that. in the end a kawasaki 1100 jet ski engine, whole costing more, might be a (better?)viable option, since they are powerful enough and a turbo would not be too difficult to install. That vid I sent, has the guy with that kawasaki at 400 hp??

. but i doubt that. Im guessing closer to 200 or so.
Anyway, I appreciate all your advice. and time.
do you have any other details, pics etc of your build? how far along are you? It would be really beneficial to see some vids?
ok, im off to do the bottom cut outs. should be challenging!