Boost + Carby + LPG = What Nozzle?

[Hadey65]

Hey all, in need of some help. Im running a Holden 202 turbo on a dedicated LPG (propane) blow thru carby setup and Ive recently installed a water injection kit. Im using 50/50 water methanol mix, running around 22psi boost and making about 500/550 flywheel HP. What size nozzle or how many cc of fluid should I be spraying into the engine as being its a carburettor and not injected I cant figure out exactly how much fuel Im putting into the motor to calculate a %. Any advice would be great. Also it is already intercooled with a water 2 air cooler and the nozzle is mounted just after the cooler, about 600mm before carby.
Thanks