That is one of those things, where who ever ported your cylinder should know which pipe the engine would need, but in a case where if a quad was bought & you dont know the specs of the engine, so you dont know which pipe would be best, then the cylinder port work needs to be degreed in to see which aftermarket pipe would match up with the porting or if one need to be custom built for it.
When I'm questioned about porting, I find out what the riders skill level is & the type of racing they intend to do & then what performance parts, pipe or pipes they have to the engine, because I do a lot of porting to match up with the pipe or pipes the riders have to save them a dollar or two.
Neil