I once drove a TD Transit which had developed a faault on the EPIC engine management system and they had removed it and just fitted a normal mechanical pump and turned the fueling up to suit. It went pretty good.

There is a company called Dronsfield Mercedes in Oldham (don't have the number to hand). They are a large independant garage who deal in Merc parts mainly but also scrap a lot of other vehicles including Transits. They may have some TD bits in stock or possibly know of some...