Welcome-

Set-back pump, for (more) interior room, 4.3 V6 & 'C' impeller ~50 mph, depending on the shape of the bottom of the boat.

The project sounds ambitious. Good luck. Need pics...

Daniel

I think the v6 Marlins were bigger, I haven't actually found much info on the hull, but no matter,
it won't resemble the original boat when I'm done.   

Making room for people and not the engine is a big issue.  Outboards are ideal in this regard.
I bought a 12JF insert pump, so the jet is moved back quite a bit. 
The pump looks to be in good shape, impeller has no nicks etc, no noticeable shaft play,
but how can I really tell if its good?  Should I dismantle it to check it out?
The tag says it has A impeller if still original.

I've been considering many different engines.  A bought a rx7 12A rotary I wanted to use,
turbocharge it,EFI, but in attempt to make things easier, I bought a Subaru EG33, flat 6,
that should work with stock efi, no turbo.   The flat 6 might make it possible to put seating
on top of it.  maybe. 

pics?  hull is in storage at present, but pic before parting it, the pump and eg33 pics for your visual enjoyment. 

I think the v6 Marlins were bigger, I haven't actually found much info on the hull, but no matter,
it won't resemble the original boat when I'm done.   

Making room for people and not the engine is a big issue.  Outboards are ideal in this regard.
I bought a 12JF insert pump, so the jet is moved back quite a bit. 
The pump looks to be in good shape, impeller has no nicks etc, no noticeable shaft play,
but how can I really tell if its good?  Should I dismantle it to check it out?
The tag says it has A impeller if still original.

I've been considering many different engines.  A bought a rx7 12A rotary I wanted to use,
turbocharge it,EFI, but in attempt to make things easier, I bought a Subaru EG33, flat 6,
that should work with stock efi, no turbo.   The flat 6 might make it possible to put seating
on top of it.  maybe. 

pics?  hull is in storage at present, but pic before parting it, the pump and eg33 pics for your visual enjoyment. 

You are going to have some difficulties using that pump. These pumps utilized a mold insert.

Curious to see how your going to get this done.

Cut hole in perfectly good hull, then made that big hole even bigger with a router.
The board to fill it slips into the routed slot. 
It seems from other posts I've found that the pump should not be mounted straight with the keel,
but angled up 5%, that is about what the existing transom angle is close.

Slow progress on this project!
I've been building the twin-turbo 12A rotary engine.  Never built a rotary before, and it took 4 tries to get the seals right,
but finally got it, now holds 14psi in the water jackets.   Still fabricating the twin turbo exhaust manifolds,
here is picture of the early going. 

But have taken a break from the engine work, and wanted to finish the hull repaint.
I've stripped all the stuff from the hull, removed all the decals and sanded it.
Now I need to paint it.   Here is what I'm thinking for the design.  Basically going orange black and white as the theme.
Got some nice burnt orange vinyl to accent my seats that I will be making.

nice color theme.  consider using a blue or neon green pinstripe to break between the colors.  it works well. 

great before and after on the boat paintjob!  loving the progress so far.

Why did you pass oh Tyne rotary

Wow, can't believe I started this project in 2014, so it has been 10 years now!  And I still have the boat and it still doesn't have an engine in it.
I am determined to get it working for the spring of 2025.  Was even hoping to get it working this month, but the Ford 3.8 V6 I picked up to use turned out to have no compression in 3 cylinder and had bad valve guides. They are 200hp and compact and light.  But no time to fix it.

My current plan is to put in a W8 engine from a Passat I picked up years ago.  It was for a Porsche 914 project, but I have sold that car,
and can't think of anything else I can put this engine in.  Being they are at this point very rare engines with no parts available, seems ideal for a boat that is not run many hours a year, so it should last a long time.  And they look awesome with the big fat cylinder heads and had a great F1 kind of v8 sound.  275hp.

I am thinking of two different issues.  The first is the coupling from the jet to the flywheel.  I have a u-joint coupler that came with the jet.  It seems it is very heavy duty. I want to move the engine further back and the "driveshaft" moves the engine forward a good amount.
I am familiar with jetski's couplers, they are much more compact.  Was thinking maybe they can't handle the power, but I looked at the newer yamaha ski's with 300hp and they use the same style of couplers.  The other idea is to use the driveshaft coupler used in a BMW, 
Any input on these ideas appreciated.

The other thing is I want to eliminte the alternator and starter on the engine, and replace it with a single motor like a hybrid system does.
I have the generator motor from a prius and am looking into attaching it on the jet input, so make the coupler on the jet side also a motor/generator, that can spin the motor to start it and also work as an alternator.  And it could also add power on takeoff for a short time.

Anyways, it may be I can't get going on this until next year, but I've got the boat all cleaned up and can do some work on it now.

Thanks for the interest.  I found an all-aluminum $200 5.3 LS4 out of a MonteCarloSS, so that is my current plan.
Life has really prevented this boat getting done so far, but have new shop now and it needs to get done.
I'm wondering how to get the water cooled exhaust for the LS and hoping I can use the 455 manifolds I have.