I have been using Sebring tuned exhaust (headers) for years. The only thing available today that's like this is the
Bursch tuned header. Instead of a muffler, there are glasspack or stinger (track only) options on the output side.
I am in the process of evaluating purchase of the Bursh glasspack, or cherry bomb or thrush. Since my engine is out now, I am considering using POR-15's degreaser on the headers first, glass bead blasting them (remove oil first because you can blast the oil into the surface), and then applying POR-15's metal prep, then POR-15 high temp paint. Next, wrapping them with titanium header wrap (not the default fiberglass everyone uses) to keep the temp down in the engine bay.
For an air cooled engine, you have to do everything possible to keep the temp down, to increase performance. Heat in an engine block arises from combustion and friction. So it does no good to allow the exhaust heat to add to the equation.