Drove it today, and even with blown out shocks, no sway bar and 14" tires it was a huge improvement over the stock t bars. Ordered a set of Hotchkis shocks today, and will be starting bbp conversion with 18" wheels and tires.
This is great to hear.
While 72blueNblue is right that the experiment had too many uncontrolled variables, I know what you mean when you expect an attribute to change and you observe something entirely different, it sets off alarms. I don't blame you for asking the question.
It sounds like you're on your way but I'll just add that I have these same torsion bars, Hotchkiss/Fox shocks and the combination seems pretty good so far. I think you'll like them.
Is your 1975 car really running the small-bolt-pattern? I've heard of some '73s (all /6 cars, IIRC) that came with SBP but nothing that late into production. Very strange.