First of all, thank you for all the information - you've practically saved me from paying for a lot of bits which I'd have had no use for otherwise!
Looks like 1275 will be the best way forward - I'll check about the carbs but might end up getting one big one up instead of the two. I have seen various references in threads on here claiming that with the exception of looking good, twin carbs seem to have no real benefit over a bigger one but I was still hoping the whole engine would have more useful bits to offer up!
BMCE Re the head...Maybe I can pick a recent one with unleaded-friendly valve seats cheapish then...Malta petrol is not exactly the highest quality and i'd rather play it safe as I want to drive my mog as often as I can

As for the gearbox - was going to try and speak to a local engineering firm to see if they could hook up the morris and ford bellhousings together before looking into buying the readily available cast bellhousing as it is not the cheapest option available yes!