The C303/TGB vehicles have many parts issues since other than the B30A motor, they share parts with Series II Landrovers and they have many unique parts as well. Other than a few that were built for municipal use, most are 24V. There have been many people who have done various engine conversions, but these are difficult and expensive. The vehicle is heavy and wind-resistant, so it is tempting to put in an engine that will overpower it. Many people who have done this have seen that the other parts are not built to handle this and they start breaking things. As an owner of one of these, I can say it is a great truck, but it has its limitations.
Cheers,
Greg