thanks for the info Hb. congratz on your record too, i was thinking of just running the stock 78 750 manifolds with flatside mikuni's and 2 750 inlet cams, only a couple of degrees here and there and much the same lift as the sifton #390
i'm oldish and have looked up the t100 tuning kit to get an idea of lengths of pipes-finish at the back of primary , short megas to about 4" finish about the back axle.
what's your low end power like, with the 390, another site says it's not streetable but I've put radical cams
in cars and put up with it
My 650 with 34 MM flat slides ans Sifton 390 cams idles reliably at 1000 rpm on the electric tach. Off idle is ok at part throttle but use full throttle and there's a bit of reversion at around 4000 rpm. Once past that the throttle response is fantastic....I think in a 750 the #390's would be ok with the proper gearing in a light bike. Perhaps messing with part throttle jetting, intakes and pipes might get rid of the reversion for limited street use..
Cams for vintage bikes like Triumphs are mostly older grinds and lack the sophisticated profiles of modern car cams.Triumph guys jockey the cam timing around to find power, but on something like a Chevy V8 if you need to alter timing by more than two degrees, it's better to select another cam from the endless list of grinds available.