keep it rwd converting to 4wd in a capri is going to be a real nightmare,gearbox wise have a hybrid mt75 made up from xr4x4 front end to give you the v6 bellhousing and a 2 litre 2wd rear end, that'll handle enough power. As for manifolds you'll need to get them specially made up and a pair of t3 turbo's will do perfectly.