hi , If CNG is the same as LPG here in Europe, i can offer some advise as I had my X converted to dual fuel 3 years ago.I could post you some pics of the installation if your interested, Steve

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2005 Toledo Blue 3.0 Beige Lthr-sport-prem-clim-autodim mirrors;;
Mods so far; rear fog lights retro-fit,ractive oval tips,titanium grille set,OEM trailer hitch,mud flaps, aux audio input,non-smoker ash tray,sub-installation and a set of the 4.8is 20" replicas with cooper Zeon 4xS.Euro clear headlights & rear parking sensors.LPG Dual fuel convertion.Chrome bezel rings,Fitted uk cycle lighting board electric hook up,Sport wheel centre re-trimmed in Alcantara,
Still luvin the ride :