My brain is hurting...

Right, im looking into the whole idea of an engine upgrade in a project defender im considering taking on. after a good bit of looking around, it seems possible, but could anyone whos done it explain to me how mating a defender gearbox to a different engine works, i know that you can buy mating plates, or have them made up, but is it effectively sandwiched between the engine and gearbox? if so, doesnt the drive shaft out of the gearbox need to be extended? also, would you be using the clutch for the donor vehicles engine or for the defenders?

any help would be much appreciated as im lost..

what engine your thinking of using would help

to be honest i think its irrelevant at the moment as its really early days, but something along the lines of a mitsubishi 3.2 or later 2.5 but for the moment im just trying to get my head around how one would generally go about it

200tdi is a good place to start, and it's a much easier job to mate up to the existing gearbox