I am UK based and have a 2002 4.4 V8, purchased car 2006 with 42 K on the clock.
Had the lpg conversion done on purchase , have now done 103k and get equiv of 33 mpg.
Well pleased ( I used to run lpg Ford Transit vans(parcel delivery co.) and frequently saw 250k mileage on the engines, with negligible bore wear.

Lez