my bruv had a tractor a 6 v system, he bought one of those 6 volt ameacan yellow coil wound batterys-- really good

Post script to this - bit late I know but I'm laid up with the lurgy & trawling thru all this useful stuff.
Same car Russ.
Jumped it once 'normally', it started fine but the battery boiled. Jumped it a couple of times since by connecting the - lead to the exhaust header & the + to the + terminal of the starter motor; battery didn't boil, started fine.
Subsequently, the battery is holding charge so we got away with that to an extent but it probably shortened its life. On the up side stripping and cleaning the starter switch on top of the starter motor has improved the starting no end
mike