The W58 gearbox will indeed mount onto a 7M-GE, however, you'll need to use the turbo clutch iirc, the n/a one won't hold the horsepower for longer than about a week!
The W58 gearbox is good for 300bhp, so as long as you're not going insane with horsepower mods, it'll do fine. You may also find this useful:
http://www4.tpgi.com.au/users/loats/...gearboxes.html