just supplied a petrol carby ( genuine ) to assist in converting back to petrol only. In australia it was common for dealer to use the original throttle body and fit an Impco carby on top of it. This way the original accellerator cable was still able to be used and the governor remained in place. If yours is like that then you only need the major part of the carby since you can use your throttle body.

Thanks everyone for the replies. I see from the replies it wouldn't be a simple thing to do. We might have a look at converting it to petrol as Bagwan suggested or possibly spend a bit of money getting the engine to start easily (once it starts it runs nicely) and then selling it and getting a diesel. Thanks again everyone for taking the time to help me.

I agree with some of the previous comments but I would expect yours to be lpg as there are very few operating on natural gas and U.S. terminology relates gas to gasolene ( petrol to us here in Australia ) The diesel engine used in that model was Mazda XA of which the numbers were not large and as of this date we as the major dismantler in Australia have not had one to dismantle. The next model H2.5 DX has the Mazda HA and as this unit does not have the same transmission as the XM series adaption would not be easy. ( we are dismantling 2.5 DX diesel units ) How about converting to operate on petrol as it should have been produced as a dual fuel machine , if not , items would be available to carry this out.

bbforks would be correct
converting gas to lpg is fairly easy
but converting from gas/lpg to diesel is a whole different ballgame

you'll need a new engine
fuel tank (needs to be diesel compliant)
cooling system will have to be compliant with a diesel application
a battery capable of handling a diesel engine starting system (usually larger than standard batteries)

you would have to make so many changes to the truck it wouldn't be worth the cost imo.
take the lift to a traders market that trades in equipment and sell it and find a diesel lift that suits your needs and buy that in its place.

I think that getting the lift starting/running good then replacing it with one that better suits your needs would be a better solution.