Just another question, has anyone made an exhaust to route the back out through the original blisters to make it entirely realistic instead of plumbing out of the bottom.
I have seen metal exhaust blisters on the net  for about $80 and there is a large Spitfire Mk9 on UTUBE but it is too big for this plane.
I have a 120 AX and am trying to make an expansion chamber behind the engine then split it into anout 6mm tuned pipes back through the side of the fues.
It doesn't take many tubes to get the same CSA of the OEM muffler but the back pressure from the length of the pipes might have an effect.