When you remove the clutch pressure plate from the flywheel, loosen the
bolts, in a pattern, a little at a time so as not to warp the plate.
Same when installing the pressure plate.

To remove the flywheel, you don't really need a flywheel lock.  I stuck
a Phillips screwdriver through one of the bolt holes, where the clutch
pressure plate went, and out of the big hole in the case which would
provide access to the drive plate bolts if it were an automatic.  That
held it securely.

While I had the transmission out, I replaced its input shaft seal as
well as the starter bushing.  If your clutch chatters right now, and the
motor mounts and transmission mount are good, then the cause could be
the clutch throwout bearing fork.  You can either replace it (and its
bushings) or dress it up where it contacts the throwout bearing, so that
the ends are rounded again.

Mike