a/.  apparently one fits a St piston liner to a K&B Torpedo .29 case.

Early Rattlers were K&B's with ST piston/cylinder and rod. Later, they made their own sandcast case, front end, and I think, back cover. The internals were still a mix of K&B and ST parts. We had at least 3 of these, here in the Pacific Northwest part of the USA. I was tied by one on one occasion, otherwise, as I recall, somebody with a ST .29rv won, mine or somebody else's. The ST's didn't break anything, except pistons, on occasion. I got best results by putting in a K&B .40 venturi, and lowering the head .040", 65%-75% nitro. Lots of power, but some safety margin. Parts were hard to get, even then. It's why I finally gave up and flew F1A for 15 years.

b/.Now apparently theres a few differant .40 cases . Anyone documented
the changes to the bypass passage.

Later .40's got bigger bypasses, of course. Around '69 or '70, they got a squish head. I reworked a '67 .40FI for a FF buddy. It ran 18k on an 11-4 RevUp and 30% nitro. He said it was faster on that prop than the "Snarly Ported" K&B .40's, which isn't a complete surprise. It really howled on an 8-8 TF Speed Prop on 40%!

c/.One presumes an early case with a small bypass would be the trick for a stunt .40 topedo .?

I tried a K&B .40 (#4055, late model stunt version). Not much power, incredibly heavy, what more could you not want? I sold two NIB and gave the used one away.

 Back to a/.  - any dead .29 Torpedo FR or RRs in the cupboard ?

No, but be aware that the FR and RR .29 had different strokes, with the FR being longer, so if you made a FR hybrid with ST piston set, you might end up with over 5cc's.

Steve