Have you measured the engine to see if it would fit inside the engine bay yet? The injector pump drive belt on the rear of the engine sits a long way back past the block and will push the oil filter forwards into the front crossmember. Not impossible to get around but more work to consider if you haven't already. The LT77 gearbox requires significant work to fit inside the tunnel of a manual car, and dimensionally similar in size to the BW65, then you'll most likely need a custom length propshaft.
The bits to convert the Rover fwd engines to rwd appear to be difficult for most people to obtain, although not impossible. I have no real experience of autos but it may be possible to get the fwd auto preferably off a Rover diesel and unbolt/ cut the gearbox section off leaving just the bellhousing and starter motor, and make an adapter to mount that assembly to the front of a suitable rwd autobox.
The bits to convert the Rover fwd engines to rwd appear to be difficult for most people to obtain, although not impossible. I have no real experience of autos but it may be possible to get the fwd auto preferably off a Rover diesel and unbolt/ cut the gearbox section off leaving just the bellhousing and starter motor, and make an adapter to mount that assembly to the front of a suitable rwd autobox.