[Moppie]

You would need an engine similar to the one your replacing.

e.g. The Toyota 4age engine was used in RWD and FWD cars, and you can swap most of the engines between FWD and RWD models. However you need to have the right bell houseings to make it work.

In your case you might have to fabricate a bell houseing (possible but expensive) then you only need worry about the in put shaft matching.
Not as much of a problem as you might think, as it only has to match the clutch plate.
So all you need to do is find a clutch plate that fits the g/box, and also fits a housing that fits the engines flywheel.
In most cases if you can't find something that all fits, you can get custom parts made (again, its expensive).

In the case of the Toyota 4age, the later model 4age's need a Toyota Hilux clutch plate to fit them to a RWD gear box.