Just asking, but what is the casting number on the flywheel. The 57 passenger and most 57 truck flywheels should have a clutch face that is about 10 inches, and when new, used a 9 1/2 clutch plate. You can use a 10 inch plate with a corresponding 10 inch pressure plate but its really not necessary. So if its a real 57 flywheel, consider a slightly larger 9 1/2 clutch. Some 57 truck flywheels accommodated an 11 inch clutch plate and flywheel. I have never actually had one of those but I understand, and hopefully someone will come along and either correct me or confirm my understanding, is that those flywheels used a somewhat specific and maybe even rare pressure plate.
If you are using a 51 flywheel, that might explain the smaller 9 1/4 clutch plate.
Make sure the raised hub on the clutch plate faces the pressure plate, and that the hub fits into the pressure plate. If it does, then install them and tighten the pressure plate bolts down completely (using a centering tool of course) and see where you are at.
A really great resource for clutches and pressure plates, and the rebuilding of OEM GM cores (better then the offshore Chinese junk that is sold today) is HR Clutch in Bensalem, PA. Old school company. They were the source for Schieffer clutches and pressure plates back in the day when the Hurst Company was located in Glendside Pa. They are a wealth of knowledge and can build or rebuild anything. A couple of years ago they rebuilt a scheiffer pressure plate, and one of their own clutches that I originally purchased in 1981. The work was spot on.
http://www.hrclutch.com/
