Is the clutch pedal return spring and the over center spring the same thing?

Modern diaphragm clutches should not stick. This was a problem in the old days. Way back in about 75, I had a 340 I swapped into my 70 RR, and decided to go diaphragm. I used a factory GM clutch out of a HP corvette 10 1/2" Worked great. Removed the OC spring and never looked back.

I am pretty sure you want to remove the spring.

You see diaphragm has no RPM centrifugal assist. B&B does that with rollers inside the cover which wedge against the PP. As RPM goes up, the rollers try to fly out, and wedge harder, pushing the clutch "engaged."

Long (Ford) act the same way except they have bob weights on the ends of the levers. Some performance Long PP have removable bob weights you can adjust