You will need the following:

Sapphire/Escort Cosworth (not XR4x4 as they are different) front hubs,
4x4 front struts,
Crossmember,
Engine mounts,
Engine mount arms,
Sump,
Speedo cable,
Speedo drive,
Front driveshafts,
Front diff with the strengthening brackets,
Clutch cable,
Release bearing,
Propshafts (front and rear),
Gearbox cradle,
Gear lever and cradle,
Gearbox mount,
Oil filter arm (the oil filter gets in the way of the engine mount arm on the N/S),
Brake calipers, discs and brake hoses,
Steering rack,
Steering coupling,
Gearbox,
Starter motor,
Sandwich plate,

That's all I can think of at the minute.

On the 4x4's there is a hump in the floor on the O/S due to the transfer box casing so you'd have to give the floor a bit of a bashing.

As for the rear diff, there is a very small difference in ratio between the 2wd and 4x4 (can't remember how much exactly) but I wouldn't think it would cause many problems.

Better off selling up and buying a 4x4 IMO.