You also need a needle bearing for the 2.9 crank for the layshaft to run on,cars with autoboxes don't have them.
Cost £5 from Ford last time I bought 1.
Xr4i gearbox will be the easiest thing to slot in,I'd be more worried about wiring it up so it runs.
A 2.9 v6 cosworth engine would prob be easier to wire up,more power,nicer looking.
iirc the pre 1992 loom is the 1 you want.