what on the bike now , an SU ?
these , I believe , use a different manifold ( with vertical studs )
and the closest substitute manifold for an AMAL
would be a later 6T or T110 . ?
is the 6T of mild enough build to still use older carb specs ?
(then 27~ 28 mm )
, substitute for the SU of the time , could be a pre-monoblok
like this ,... probably don't want to go here , this is over 300 £ ( and seems rmildly jetted ? )https://www.feked.com/amal-276fg-1at-pre-monobloc-11-16-carburettor-triumph-6t-thunderbird.html
specs says 1+ 1/16" , which rounds up to 27 mmAMAL
1+1/16 Carburettor - Triumph 6T Thunderbird
Triumph 650cc 6T 1951-1953
140 Main Jet
107 Needle Jet