If you dare to experiment...: the Allen Millyard engine used to be a single...he made it into a V2. Hand-work. He has done a bunch of more advanced engines too. All hand.made.
These days, most people have forgotten how engines, or complete bikes were made in a shed 50+ years ago. Not by big factories. That is what I try to tell.
Please see the movie; "The worlds fastest Indian", and "Britten, One Man's Dream", - then go get your hands dirty!
BTW; Honda produced the small 125 twins WITH dual-carbs, and 15-17Hk @ 11-11500RPM. NOTE; they are 180 degree engines, with dual point / independent ignition systems. Not that it should make power, most probably due to engine-balance, and higher RPM capability. (because of the 180 deg. layout, camshaft will also differ/not compatible with "CM/CMX" - 360 degree twins).
In comparison; The CM/CMX(CA) 125 with single carb; 10-12Hk
Whilst I've seen The World's Fastest Indian, I think I'd rather watch HEAT, then go rob a bank... Mainly because HEAT is my favorite movie, it is just awesome.
I was also kicking around the idea of building an LS V8 engine, with a TVS blower, and then squeezing it into the Rebel 250's frame but changing NOTHING else. I happen to work for the company that produces said blowers, so somewhat easier to procure. Sounds like a simple, easy and logical project! I would tell all the other motorcyclists I meet that it is just a stock Rebel 250 (ignore the sound coming from it, I think something may be working loose).