Cheers mate, interesting read. I've never done much with the old 12v, there are barely any left now. I've probably seen more of them in old Hawk Stratos replicas than I have in Alfas.
No probs, I'm having trouble finding bits and bobs for the 12v because of their rarity, which is why I thought it'd be a useful comparison to make - common wisdom says they're completely incompatible, but it looks like there's a lot of parts interchangeability apart from the heads / oil pump, and presumably the crank.
E.g people often say the sump from a 75 won't fit on a later 12v, but from what I can gather, excepting the oil pump issue, the main problem is the front panel with the crankshaft seal in it. But if the panel from a 12v will just bolt on, that's not such a problem after all