don't know whether you could bolt it up or not, but I don't see the point, the carb is like 10 to 12 mm bigger than the 200x. You would have to have a SERIOUSly built 200x motor I don't think you build one beefy enough. I just read a article last night in my old dirtwheels on the curtis sparks powroll 200x's from 85 and 86 and they both were running high compression pistons with a bigger bore, lots of exhaust and intake porting, longer crank, racing cam and exhaust and they still only had a 28mm mikuni on them. Stock 200x is 22 or 24, and 350x is 34 I believe.
73 cr250m elsinore, 85 atc70, 85 250r flattracker, 87 250es bigred, 86 tecate, 2004 gas gas de300