for me id go for small block ford idealy late 302 or 5.0 out of a mustang with its T5 box or a small block chevy ideally a 350 with 4 bolt mains, both got plenty of tuning potential or if you want something newer LS chevy lump or you could go Audi or bmw wouldnt bother personally these days with a rover lump, my brother is putting a SC jag V8 in his mk2 cortina with a adapted lotus carlton 6 speed behind which we think when mapped under sc under driven etc should see 500bhp