Erm.....why?.....the gpx250 is a 38bhp engine (or thereabouts) the carbs are probably way out in terms of ability to breath the srx6, when you consider each carb on the gpx is fuelling a 125cc cylinder.....no match for a bluddy great 600 pot!
you'd be better looking for a pair of 34mm or 36mm mikuni/dellorto/amal carbs .. or get a dynojet kit for the standard YPVS carbs, at £70ish a bit pricey for what you get, but considerably less than the cost of replacements (and all the associated work/modifications). and does apparently achieve reasonable results.