Tom - Time to change your thinking to current thinking on trannys I'd bet. A long talk to several tranny venders just may give you a new way to think about your problem.
We used to think in the muscle car days that built heavy duty TH400's, C-6's and Hemi-727's were required to take the hammering of big engines and fairly heavy cars in the 70's. That was 35 years ago amego. We now know that those trannys broke BECAUSE of the heavier components, and futher more, when they broke the heavy duty stuff does more damage. Thinking in that new direction, I give you the the racing powerglide. Lightweight, Can take over 2000 horsepower and live, runs cooler, looses only about 10 horsepower to drive line power losses And so on yada, yada. The list goes on and on, believe me.
So what's that got to do with you? Using the above light weight components thinking used in a glide, a C-4 can be built to handle ANYTHING either one of us can dream up for use in a Cobra. I've been saying for years that built C-4 is the right auto tranny to use in a Cobra regardless of powerplant used. Your new C-4 would be smaller, lighter, transmit more power, run cooler, and if built right, still have the abiliity to handle more power than almost all C-6's.
It won't be cheap though. And in my mind Coan transmissions is the best there is, both in racecars and in street trannys. Time to switch over a purpose built unit, and quit trying to modify junk to work. Hint: A very short tailshaft housing for C-4's was used on/in government mail jeeps and in a few other small cars down through the years. Those guys are around and are perfect for Cobras. That short tailshaft housing would also make room for that future gear-venders overdrive unit if you were inclined to think that way. Time to do some research, and go get em'.
www.coanracing.com
cobrashock