Re: New 4 stroke Build Honda GHX50
welcome to the forum, IronHorseBikes! Looks like you're building a solid runner!
My brother has a GXH50 and I have the Huasheng copy of it. We both use the same type of exhaust:
Header cut from a chinagirl 2-stroke exhaust, 32-36" of stainless flexpipe, and a Briggs 5-7HP muffler.
Probably the best-sounding and best-breathing exhaust you can put together for these.
Good luck on the intake manifold. As it is, these have a plastic spacer roughly 3/8" thick that serves as the manifold. But it works well.