Bob,
Have you tried phoning Lew? I think I heard he doesn't much like email. BigIron, any ideas? Lew's Silver Fox is a gem, worth reaching him about it.
The 1970's C-Series ST 35's, as I hear, came in two versions - flat-top piston and baffled piston. The baffled-piston engine is considered much more suitable for stunt than the flat top. Look in the exhaust port with the piston down: the baffle - or fence - should be obvious if it is there.