Speak to Steve Scott at A1 Rally Sport mate - he's doing my RWD Fez, which uses Cossie running gear and front suspension / brakes / hubs etc. and a Watts linked Baby Atlas with Mk2 Group 4 suspension out back- exactly the same as what you want mate... I'm running a CVH in it but will prob swap to a Cossie at a later date...
£20k? NO WAY MATE! Speak to Steve...
Cheers,
Ben