ive had a 421 mani on my 4efe an it lost far too much back pressure mate... i dont think it'll be running 100bhp with the inlet and exhaust mani's only, your probably looking at an increase of maybe 3-6 bhp which would push it up to 78-82 bhp. if you had quad throttlebodys you may get a tidy little increase, altho all the power would be top end. over in australia they tried a fully progamable ecu on a 4efe which already had a 421 manifold, and the increase was 10%. thats with a £600 ecu!! i dont want to piss in anyones pool or anything, but i just dont think you'll get a decent pow