I agree that in certain instances and to keep the old school theme, noise and look, u just have to take a hit at the pumps. But there are so many tried and tested options, a zetec on bodies should be fairly economical, but given ur car, which should in great british hot rodding tradition have more than 4 cylinders anyway ... What about a late scorpio lump with a 5sp box. It drives most of its time on tick over and a mate with that set up says its 30-35 mpg on a run.