SVXNUT

Hi out there, have not had much luck in general, so someone pointed me here!!.
I need to know which Legacy spec gearbox will mate with my SVX 3.3l, and if it will hold the 600hp that I am aiming for from a twin turbo engine rebuild that I have planned.
I know that there are alot of Man converts in the states, but I am having no luck from there webmasters as to which box they use.
I have found evidence of turbo conversions running 800 hp that were done in the late nineties, but the info is now out of date and the posters uncontactable, but as supercharger kits for 390hp are still available of the shelf, I feel that if I throw a few quid in the direction of one of the tuners over here 600hp is not unreasonable (AS you imprezzas are easily getting 200hp per litre), and you know what American car tuners are like!!.
I have £10k set aside for the project so I am serious. I am a courrier for a living so can't afford to drive an imprezza as they attract cops.
I have already done 140mph in my SVX and it has 108k on the clock and has never been Modified.
Hope you can help.