JTSpeedDemon
2019 Build Off Winner!
Great news! I contacted EC Carburetors, and they’re making more Briggs to Mikuni billet manifolds!! 
They said they’re redesigning it without the angle per request, hopefully that won’t cause fitment issues. But this means there’ll be a commercially available Briggs mikuni kit!!! And it won’t be that much more than a GPS kit for a clone(it’s about $110 for the kit, $45 for the bare manifold)!
Look at that billet beauty! It's quite a piece!
https://www.eccarburetors.com/slide-carburetors

They said they’re redesigning it without the angle per request, hopefully that won’t cause fitment issues. But this means there’ll be a commercially available Briggs mikuni kit!!! And it won’t be that much more than a GPS kit for a clone(it’s about $110 for the kit, $45 for the bare manifold)!

Look at that billet beauty! It's quite a piece!
https://www.eccarburetors.com/slide-carburetors