My grandfather is rebuilding his Volvo Duett and I'm helping rebuild the engine. The B18 engine is very much original, I doubt it has ever even had it's head open. This time I'm not looking for outright performance though, but rather best usability in a car intended for heavy loads. What bore/cam/combustion chamber would be the best? I've also got almost all the different carburettors used from 1964-1973 at my disposal from Zenith fixed jets to Strömberg singles to SU doubles.