Hate to burst your bubble David but Centerforce ditched the flyweights well over ten years ago when Valeo changed pressure plate design. I stopped using them after that because you are paying $200- more for a stock Valeo pressure plate and a disc with "improved" friction material. It can't justify the increased expense.
I agree it's probably a pressure plate issue but with an LS1/3 or 7 installed a soft clutch pedal is probably wishful thinking and since everything is different/modified I can't be of much help here. I don't sell that exact "hard core" design anymore but could do a small run with my machine shop. I switched from boring oversize to brass sleeving but could easily do both at slightly higher cost for the larger stainless piston. I don't think it will help enough with the pedal effort but will last farlonger than the normal replacement part and give better disengagement.
Rob