Getting the clutch set up and prepared sometime soon and looking at the flywheel(early) the X mark on the edge of the flywheel am I correct on saying that it is the light side or the heavy side of the flywheel. My memory is that it is the heavy side? I would be looking for something relative to that same marking on the pressure plate to align the two.

"Been there and done that! Well Not everything.
65 500 2dr Coupe
63 Greenbrier

It would the best to have the assy checked for balance. Yes what your saying is correct but due to production tolerances it could still be out of balance. Or if the pressure plate was ever rebuilt the X is probably in the wrong spot now. I believe that GM marked the heavy spot of one part and the light spot of another. Years ago when I worked for Subaru they marked the heavy spot of both parts and you were to put them as far apart as you could. I have talked to some people who lined them up like you would normally do and had a vibration.

RJ tools
Salem,Oregon

This does not apply in your case.

But, balancers put reference marks on pressure plate / flywheel to indicate where they should be aligned when they are balanced together.

There is absolutely no reference to any markings on the pressure plate having any significance as to where to place the two units togetherin the factory service manuals. I have never aligned any marks and have never had a balance issue except on bolted flywheels.