I hope you continue to update this build thread on a regular basis.
keep the pictures coming for all the work as it progresses.

this is going to be an awesome project that all of us would like to follow,
and i think it will be successful.

It's great to see someone trying something different with such a proven hull. Look forward to reading the updates.

RR

Boat need new transom to fill 3 drive holes and 6 exhaus holes. I need fill notch partially that surface drives can fit.
What you think, is it better fill total or just so low that drives can be mounted?
How about drag and transom lift if I remove notch completely?
There will be more space in engine room if notch is removed. Engine, transmission and crossbox left 4” free space to bilge at lenght direction.

What was engine originally used for, and what is RPM when completed?

he said its from a tank,engine from a T-55.

https://en.wikipedia.org/wiki/T-54/T-55

Yes its T-55 tank engine, T-72 and T-90 (latest russian tank) share same engine. T-72 was supercharged 780hp and T-90 1200hp. Tank engines are low power vs diplacement because cooling is big problem without driving cooling air flow and heavy armoring.

max rpm stock is 2000, my P pump governor is set 2500, it start pull fuel of at 2350.

You are on the right track trying to calculate how much of the notch needs to get filled in. The drives will need to be mounted pretty low on the transom to work best. When in doubt I would error on the lower side than higher. Hard to explain in text but if your ball socket has an 8" diameter, and it's mounted flush with the bottom of the boat, then the propshaft centerline is about 4" up already! There's more to it than just that but it's an easy way to visualize why mounting a shaft drive like an Arneson low on the transom is so important.

What will your propshaft centerline be? 20"?

Crossbox is 0.55:1 overdrive and six speed transmission 3.57-0.65:1, but i don't want use 5. and 6. gears. 4. is straight 1:1, it can handle more torque than others, power goes through transmisson by two shaft, other gears just one. power loss is also lower at 4. gear. Propshaft speed is 4360 at 4. gear. My props are Rolla 33x16.5 4 blade, I know diameter should be bigger, but I try these first. So expensive to try and go wrong.
Engine max torque is about 7000-8000Nm, so I think there are no spooling issues

Offshorexcursion, you are right, I need bolt drives so close bottom I can. But my question about notch mean notch between drives? It can be there, but is it nesessary?

Centerline can be everything between 17,5"-25", I think closer together is better.

Picture show crossbox water cut plywood modeling piece, you get the idea...

This is fantastic!!! What a project