Doc,
Speak with Mark Frisby @ Linden Special Vehicles in Wellingborough on 01933 670 980
These guys are very, very good. They supercharged my fathers HSV (now has over 530bhp)
They specialise in Holden HSV's/Monaro's but perform bespoke work on all cars. I know for a fact that in the past they have supercharged a 4Motion, which went like absolute stink.
Supercharging is their 'thing' and they always have at least two cars in undergoing the full works - this place is a proper engineering outfit, milling their own brackets from solid aluminium etc - the installs look factory when finished, very very neat indeed. If I were looking at undertaking a porject such as yours, these would be the first guys I spoke with.
I really do think that it would be worth giving them a call and talking through some options.