Taking a Citroen transaxle above 300hp isn't just a matter of the CWP rotation. You will also need to strengthen the housing to keep it from flexing and causing all kinds of problems with the gear stack and output housings. Not to mention additional forces due to increased braking requirements. With inboard brakes, those forces go into the gearbox far more than the suspension. When Lotus started building cars approaching 250hp, they changed gearboxes rather than trying to bandaid the Citroen.
I looked at this problem when I started FrankEnSPRIT. The idea was to put a GM injected Emme engine into an '83 Esprit, as I was expecting my '83 engine to expire due to crowned cast pistons. The deal I got on the Emme engine was far less expensive than even the parts to rebuild the '83 engine back to spec. I quickly came to the conclusion that the tires/wheels, brakes, gearbox, front suspension, cooling system, and because of brakes and gearbox, the rear suspension weren't going to be up to coping with the increase in horsepower. The solution was to build up a '91 frame with a high-torque Renault 'box and a bunch of Lotus go-faster bits from Sport 300, Sport 350 and V8 models. It's getting closer to firing up, so one of these days I will find out if I made the right choices. On a side note, that '83 engine just keeps motoring on.
'83 Esprit Turbo (The Fabulous Trashwagon)
'87 Esprit Turbo (FrankEnSPRIT)
'90 St Tropez Turbo
'04 Boxster S
'05 CO Elise, LSS, Touring, Hardtop, among others