47mm ??? that seems rather odd , why do you want a 47mm? ...why not a standard size like 44mm,46mm or 48mm ?
have put msd unit in to go with my protec pipe an want more low down was sugested to put a bigger carby 0273069202
If its a single carb blaster then you need to put on a wetjet intake manifold you will have to get the 46 that comes with it or you will need to fill the holes in manifold from the old carb studs and retap ( very easy job) then put a single 48mm novi on this would be the ultimate setup for a single carb blaster and it will rival all but the best twin carb blasters