totally possible with mods. if you want a really reliable bike, you could just put a 16/16 dellorto sha, bigger jet, high flow air filter, a biturbo exhaust and high gearing to hit 50. it would take you about a minute and a half to get to 50 but if u need to go 50 for long commutes with no lights it will work great.
if you need torque too for city riding, and still want to hit 50 your are going to need a larger cc cylinder kit. that will cut down on the life of the clutches, fixable but it will happen.