Read this and you'll be able to fix your issues. I did this to many A-bodies having your same problem and they shifted like butter even at a complete stop. Also if you installed a Diaphragm clutch you must remove the over center spring on the pedal assembly. Been playing and street racing these cars since the 70's. There are 2 different clutch pedal assemblies used. With a borg and beck three finger pressure plate you must use the heavier spring red which calls for the side brace used on earlier assemblies. If not start doing squats to strengthen your legs.
https://www.motortrend.com/how-to/mopp-1012-four-speed-a-body-clutch-pedal-adjustment/
The red spring style is 6 inch the blue spring style is 5 1/4.
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