the new ones that should have the old calibration would be the current 4781C C for classic .
personally I would mooch a good running 4781 from a friend and try it . they work well but they are different from other double pumpers in having about a .180 downleg booster and somewhat large jets . both those things were done partly to compensate for a relatively large main venturi , 1.5" , and 1.75 throttles. if you ditch the power valve in back as you would for drag racing then you would use 82 pri 88 sec and go DOWN from there .
"either we're lost or these woods are FULL of studebaker truck fenders !"
unknown dirt biker