Adding a clutch pedal

[eric8]

I have always read that on 67-72's, "autos and manuals used the exact same pedal box. GM just slid a clutch pedal on the end of the manuals." Well I now have located a manual transmission complete pedal box and pedal assembly, and they indeed appear to have a small difference.

If you'll reference the attached pic, I am pointing to part of the pedal box that is not part of the stamping on the original auto pedal box on my 72 C10. This stamping is where the very heavy clutch return spring attaches. Why are there two return springs?

I'm doing a T56 hydraulic clutch swap. Do I need both return springs? I'd like to keep the original pedal box in place and just add on the clutch pedal if possible.