"Guest" is spot on here. Don't just go trusting any one with your pride and joy. fitting a carb is easy, but getting it to work properly is not.
Crosser shops seem to be far more at home messing with strokers than your average high street bike shop. They've always got the bikes in bits fettling this and fiddling with that, so they're a good place to go for info and assistance.
They won't even mind if you ride your NSR through a muddy field on the way to the shop........maybe!