Hi all,
I leave in France.
I use to have some 911 (3.2l, 993RS Club Sport, 993 RSR, 993 c2)
today I am on another project : 917K Replica.
with a mid mounted engine - the reason why i am asking my question here-

My engine will be a high rev/high power aircooled 3.6l.

I have planned to mate the engine to a 915 gearbox with flipped R/P. but I was told by my mechanic that the 915 will not handle the torque. even if I improve oiling and cooling and add a wevo bearing retainer.

I had a G50 (which I swap to the 915) as it was not usable. impossible to flip R/P. and flipping the gearbox is not acceptable to the CV joint (too much angle) .

I wonder if any one of you have tryed to install a cayman 987.2 gearbox (G8740 to be precise, not the fisrt gen) on an aircooled flat6 ?

Is there any kit available ? (adapter plate)

Bonjour!
Lots of variables. I would say it depends on how much hp and torque the engine will produce, the use of the car (street/track/both) and how often you're willing to rebuild- refresh the transaxle.
For my money, the 901 tops out at 200ish hp. A 915 @ 300, a G50 can be built to handle several hundred hp. I know someone who built a GT40 replica that uses a flipped over G50 mated to a very nicely built 302 and it works fine.
Outside of those choices you're into the world of race boxes such as Hewland, etc, which can be bullet proof, but also may be dog boxes, etc. Fine for track but a bit much to shift on the street.
Clutch / flywheel adapters and combos can be had from Kennedy Engineering. Maybe transaxle to engine adapters too. I imagine they'll build about anything if you've got the budget.

We put aluminum 915 boxes behind built 3.6/3.8 engines all the time. Is it as strong as a G50, no. Will it work great, yes.
Here’s a Peter Dawe (look him up) built 3.8 with a good 350hp in a 81 SC. Customer has been driving it for 3 years and is in the shop for MCS coil over shocks and big brakes. The engine pulls like a freight train. I have a good 100 miles in it, test driving to make sure it’s all sorted.

I do have a Peter Dawe built Carrera trans with a factory cooler, if you are looking for a trans for your 917. Also an SC trans with lsd. I can also build with custom gears if you are looking for something special.

*Dawes Motorsports doesn’t have a vapor blast machine so the case isn’t “pretty”.

A 915 can be built to handle it as mentioned.

Boxster 6 speeds have been put behind mid mounted aircooled 911s, but it doesn't bolt up (different bolt pattern), and there's no kit that I've heard of.

PS - I also have a rebuilt 930 turbo trans. It's definitely up to the task and can be inverted. We ship all over the world.