If it's a DIsco you'll find the gearbox longer than what's fitted, so you either move the engine or change the props and crossmember, stuff like that.
The shifter is cable on the 4 speed, so not a big issue but you will have to provide 2 oil coolers for the gearbox as a minimum (I have 3) and you have to fit the right 'box for the engine ie no TDi with a V8 box.
Obviously the V8 is best with an auto otherwise I'd recoment the later 300 TDi auto, the later ones had EDC which gives a bit more power at the cost of electricery and expensive injectors, a mechanical TDi can be tuned to give more power at the expense of emissions, which is why LR went for the EDC.
My sister has a mechanical 300 TDi auto and though a little sluggish at times it's a good truck, tows very well and quite good on fuel.
