This is the pump mine used https://www.ebay.co.uk/itm/Water-pump-electric-for-water-Charge-air-cooler/323947790562?hash=item4b6ccb00e2:g:bHwAAOSwAPpds3Nm
I think it is identical to what proalloy still supply https://www.ebay.co.uk/itm/CCLEXIGESKIT-Pro-Alloy-Lotus-Exige-S-Charge-Cooler-System-Complete/283341100294?hash=item41f8721506:g:DHEAAOSw6S9cPzZ9
The claim of 20hp was gains in mid range rather than specifically peak HP, but the difference was clear when I got the car back, I always felt it gained a lot in midrange torque and would also give you a consistent 20hp gain rather than what was more likely a 20hp loss from the engine pulling timing due to increased inlet air temps which always made the engine feel flat when it was heat soaked.