Re: XD ute
XD's and early XE's were factory available with 351C's.
To run on petrol, you will need to have any pollution equipment fitted and operational. (if i recall correctly its only a carbon cannister on the XD)
For gas...as suggested above, it needs to be certified by a fitter. Gas as we all know can be a little dangerous. A decent fitter will show you how to test for basic leaks and system integrity...IF you bother to ask!.
The basic test involved, should be done every service, and surprisingly few mechanics bother.