Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
I use CB750 carbs on my bored out CB77/72, they're about 31mm I think so 32 Amals will work, you will have to put a lot bigger main jets in to counter the slower air flow rate.
I seem to think that Read-Titan of Leytonstone used to fit Amal carbs to their race kitted CB250's with their 325cc Hepolite conversions and their own camshaft (CB350 not available in UK until 1972 'ish) ... I think Jock Kerr worked for them too at one time so hope to God he had nothing to do with it Here is (I think) one of their CB77 conversions with Amal carbs on it. (Attachment Link)