The Cinq Sporting box will do just fine. If doing this on a 899 Cinq, be very aware that you should fit Sporting suspension (at least!) the ARB from a Sporting and think seriously about upgrading the brakes. You'll also need a sporting gearchange mechanism and complete exhaust system.
ive got a sporting. iv red about puting the engine in and done a couple of replacment engines on puntos. put i herd somwere that the sporting box will be better.