<<(from George) Chris,....Have you ever put a thermocouple under the cowl
  after shut down to see what the temperature goes up to on a hot day in
  still air, after about 15 to 20 minutes?   I am thinking about things
  like wiring and ignition harness temperatures.>>

I was wondering more about the temperature of the plastic shroud itself.
Being very close and directly above the cylinder heads  I assume it would
get very soft during a hot soak.  True?  Should it be made from aluminum?
I'm less worried about wires and such as wire insulation is silicone and
should take it.  I'm not sure the mags would get any hotter inside the
plenum than behind the engine, but that is pure speculation as I have no
data.  Also, is there any reason to join the two sides of the plenum?  Why
not build two small plenums, one on each side?  Also, one of the links from
a previous post described a "RTV BID."  Did they really mean impregnating
cloth with RTV?  I assume that would make a flexible structure?  I was
puzzled.

Gary Casey