Centerforce Duel Friction Clutch

Trying to find some info out for my dad. He has a 69 Roadrunner that he has been running an 11" Centerforce duel friction clutch in for quite a while. He had taken the spring out becasue he was told it would want to stick to the floor with it there. He did have that trouble at the track when power shifting several years back.

He is wanting to know if he should put the spring back in or should he have a different pressure plate or different clutch altogether. The clutch is very hard to pedal. He likes how strong it is and he just looked at it and everything looks good but would like it not to be so hard to press.