Forgot my calipers at home yesterday, so still no flywheel measurements. Sorry!
I will get them when I get home today.
In the meantime, here is some good info about the W58 and R154, which are the 2WD versions.
There are many different versions of these trannies, and nearly all have interchangable parts among the series (W to W, R to R), most importantly, the input shafts.
These are the best candidates for us.

https://www.miataturbo.net/attachmen...ine=1454600151


W58 top, R154 bottom


https://www.miataturbo.net/attachmen...ine=1454600151


W58 top, R154 bottom


https://www.miataturbo.net/attachmen...ine=1454600151


W58 bottom, R154 top


https://www.miataturbo.net/attachmen...ine=1454600151


W58 pattern


https://www.miataturbo.net/attachmen...ine=1454600151


R154 pattern

https://www.miataturbo.net/attachmen...ine=1454600413


W58 width @ sandwich plate ~8.5"


https://www.miataturbo.net/attachmen...ine=1454600413


R154 width @ sandwich plate ~9.5"


https://www.miataturbo.net/attachmen...ine=1454600413


W58 overall length (from bellhousing mounting face) ~22.25"


https://www.miataturbo.net/attachmen...ine=1454600413


R154 overall length (from bellhousing mounting face) ~22.25"

https://www.miataturbo.net/attachmen...ine=1454600974


W58 input shaft length ~6.0", R154 input shaft length ~6.75"

https://www.miataturbo.net/attachmen...ine=1454600974



W58 top, R154 bottom


https://www.miataturbo.net/attachmen...ine=1454600974


(left side) W58 left, R154 right

Excellent info, thank you! If someone could compare Monk's dimensions to an NA/NB transmission to confirm the viability of this idea, that would be immensely helpful. Looking forward to test fitting one of my plates on the R bellhousing!

Do you already have a plate made?
If so, I have a BP and each kind of tranny already pulled.

Edit: Derp, just reread your last post. Proceding as planned...

Um. This excites me

The only plate i have right now is installed in my car at the moment.

I do however have a BP short block in my basement. So once i get the plates in it'll be pretty easy to set the deck level, bolt up the plate & bellhousing, and see how everything lines up. I assume the BP is in fact level side-to-side when installed in a miata?

BP is level side to side.

NA/NB transmissions are the same.

This also excites me. Arent r154s good for like 600wtq or something.

Wow, those trans would hang down like below the block. Can you get a measurement from input shaft to the bottom of the trans?

Also they would need some serious shifter moving. Like 10"

Yes, the r154 is bulletproof.
Even the W 58 has been rumored to handle up to 450 horsepower, but I would say 250 is more reasonable.

I will see what I can do about that measurement.
The front to back measurements in that picture are from where the bell housing meets the body.
I would actually expect the lengths to be very similar.
I will be able to tell you for sure in about an hour.

Also, I don't know that the W Series trans were ever put behind a v6, but it did go behind a 7mge and 22R.
I have both bellhousings if you would like those as well.

I'm fairly certain the 7m and 22r have totally different bellhousing patterns with no chance of bolting to my plate, so no need to send those.

My 6 speed measures 24 and a half inches from the bell housing face, and 33 3/4 overall.

I put a T5, miata 6speed, and a W56 side by side, and the differences are pretty striking.
My phone is too much of a potato for low light pictures, so I'll post some in the morning.
If a T5 fits in the tunnel, I would think a Toyota trans will fit just fine. The T5 is 9 1/2" at its widest point.
More measurements to come, but it looks like the Miata tranny and the R154 are pretty damn close to the same length.

I should have realized this based on the length of the input shaft, but I confirmed the 3vz bellhousing is 6.75" deep, making the overall r154 length 29".
That's about 5" shorter than the Miata box :sad2:
I'm not sure how you would make an extension for this box.

So, i googled, "R154 shifter extension" and there appear to be several options, here's one of them:

R154 Shifter Extension for MK4/SC300

I finally got what you originally asked for.
Hopefully you can tell by my shitty drawing, but the distance from crank to friction plate is 33mm, and 16.5 from the crank to the bolt flange?
Whatever the hell you call the flat part where the bolts go through.

https://www.miataturbo.net/attachmen...ine=1454845177


https://www.miataturbo.net/attachmen...ine=1454845177

Crankshaft side for posterity.

https://www.miataturbo.net/attachmen...ine=1454845436

Thank you! The drawing and measurements make sense.

What i'm not sure about is... what clutch is that flywheel intended for? It looks very small in diameter like maybe a twin disc racing clutch?

Yes, twin disk clutch.

Specifically this one:

https://www.miataturbo.net/attachmen...ine=1454939097

It will work with most 7 1/4" clutches though.