Where is your pressure plate from? Maybe the finger to flywheel distance is too short. I think there is a spec for that height. If it's too short the overcenter spring will not return. Luckily this gets better as the disc wears.

If your bearing clearance is good and the engagement point is good. I'd just run with no overcenter spring. Just confirm the release fork spring is strong enough to hold the entire linkage assembly off the fingers.