T5 box has fitted fine into my 1.6 3 door shell, just had to drill holes in the floor and drop bolts through sitting on 4mm strengthening plates as the tunnel/floor is only thin skinned and doesn't have the extra mounting point on the underside that a Cosworth does have, you'll then need washers/spacers to line the gearbox engine and prop shaft up, something that I'm still yet to do as the propshaft sits at quite an angle ATM, however the Cosworth propshaft mounted into the same points on the 1.6 shell just fine didn't need any mods there, can upload some pics for you later if you like?