I have been using propane/lpg on larger V8 vehicles for years with great success. When you talk about using fuel injection, are you talking about a dual fuel setup? I am not aware that there is any way to use fuel injection with a single-fuel lpg setup; lpg requires a mixer which functions much like a carburetor. Fuel injection systems can certainly be used as the gasoline component of a dual-fuel setup, whereas twin SUs would be a serious challenge. Single-fuel lpg has advantages, other than the obvious simplicity; you can modify your compression and timing to take full advantage of the fuel. It is not a simple matter of advancing your timing; lpg prefers a completely different curve, advancing much more quickly at lower rpms but not at higher. LPG will also reward a high compression ratio, up to 11/1 in a low-stress application (passenger car instead of truck, for example.)

LPG (propane) is considerably cheaper here in Alberta than gasoline. It also runs much cleaner by nature, as you mentioned. Let us know how it works for you!