All good info, thanks for the tips. I have a 68 350 that came with a 2 barrel. I'm wondering if there was a difference between two and four barrel cables and/or pedal assy. The previous owner put in a different 350 with a quadrajet and when I bought it, he said it never did make a whole bunch of power. Found with the pedal to the floor, it just fell short of starting to open the secondaries. Might be something to check.
Thanks for these additional perspectives. I've rebuilt my Rochester 4BBL and eliminated the restrictor flange on the secondaries and rebuilt my stock throttle linkage to remove the play, so I can eliminate these two factors.
Remaining factors are: a. the plastic bushing on the firewall bracket is worn and has flex, and b. the accelerator pedal which I cannot adjust (may be welded in place!). I'll replace both the firewall bushing and the accelerator assembly to try and get to closure.
FWIW I have seem a few aluminum accelerator assemblies that are more adjustable but $20 is a lot for a gas pedal and I do not want bling under my feet for a weekend driver. I will try the $60 assembly on Classic or Firebird Central (cannot find better quality).