It would make for an interesting dyno test.
Build something big enough, capable of making enough power to exploit any possible gains the pinch itself might offer.
Something like an 11-12:1 408/416, .600-ish lift cam, decent single plane intake, nice carb, 1-7/8” headers.
Take a set of TA heads and do a nice port job on them(260+), but don’t make the width at the pinch any bigger than what could be done safely without breaking through the pinch area of a non-TA J head.
Dyno test the motor.
Pull the heads, open the pinch area as much as is easily done without worry of breaking through with the TA configuration(no additional work...... only the pinch area)..... reinstall heads..... retest.
