Merlin/Meteor fuel cut off MK VIII Replica

Really stuck at the moment, I do not want to trust the mag switches alone to stop the engine, The Meteor unlike a car engine has mags and runs under its own steam so to speak you cannot cut the electrics, the mags are earthed to stop the engine. If this fails the engine keeps going.
Because Merlins have supercharges you have to cut the fuel before turning the engine off otherwise the fuel mix with be forced out without being burnt and catch fire on hot exhaust stubs. What i need is the fuel cut off from a merlin or something that can cope with a two gallon a minute fuel flow, if anyones got a suitable valve (I need two) please let me know.

Merlin Pete HELP 😀 😀