not the most correct place to ask this, but hoping someone will know, or can set me off in the right direction.

I Know an AJ16 4.0L is a variant of the earlier AJ6 design, But how interchangable is the flywheel, clutch and transmission with the earlier AJ6?
and with the XK even?

I have a line on an AJ16 engine, but it would be a hassle getting the wiring loom and everything else, and I would like to do a dumb (no computers) automatic, or possibly a 5 speed trans.

It might be too much to ask, but I have a rebuilt original auto box and torque converter that came with the load of parts when I bought my 3 mk2's. if I could use this, that would be ideal.

any advise?

There is no commonality at all between the XK and AJ engines and transmissions. If you want to connect a Mark 2 gearbox up to an AJ16 engine, then extensive engineering work will be necessary.

too bad, thanks though

there could be a box out there that's fits,
I have a 4.2 v8 and no manual gear box made for it,but I have a speed box that fits know mods,and made a flywheel for it,

Even so, you could still use a more modern trans and "adjust" the driveshaft instead.