Clueless in Seattle (Petersburg)
I'm clueless on that exhaust system. In so much as the radiator, however, the square inches or square millimeters of surface area have to be adequate for dispersal of unwanted heat. Considering the size of the R3 radiator, I would ascertain that Triumph engineers allowed little excess surface area for the heat transfer. The frequent cycling of my cooling fan attests to that.
I'd be willing to bet that a custom radiator would cost plenty maybe prohibitively. Besides that, you'd have to design in hose connections and routing. Way too much custom engineering for the end result. Better to blow a wad on a full custom exhaust and then market it to the multitudes. Some time ago, I wrote a post about tube benders. To make a first rate set of headers as well as the exhaust system without decreasing radii bends which result in gas flow turbulence, you need a mandrel bender and an entry level mandrel bender will set you back around 25K. The Midas muffler shop's bender isn't a header bender. Neither is any bender sold to the general public. They are all decreasing radii benders. You need a mandrel bender or as a second choice a radial draw bender (that's what I have). The radial draw causes a minor amount of radii constriction, whereas the mandrel doesn't cause any. I have 5K in my radial draw and each diameter of tube requires a new die set.
The radial draw is what dragster frame builders use as well as shops that build custom bike frames and roll bars. You can get in the mid 20's on a radial draw with hydro-mechanical actuation and mid 30's with CNC control. The mandrel starts around 25 and goes over 150 thousand, depending on the complexity of the controls.
Today, custom work requires a big buck outlay with only a slim chance for a profitable return, that is, unless you are Corbin......