Hello from Maine,  Opening unit valve blocks such as Ampico valves
is actually quite simple.  First, remove the cork gasket, then sand
the shellac sealer (by hand against a sheet of 100 grit sandpaper on
a flat surface) until the glue joint line is clearly visible.  It is
not necessary or desirable to completely remove all the sealer.

When the seam is visible all the way around, take a new utility knife
blade and very carefully place the blade so the edge is exactly over
the glue joint and perpendicular to the surface.  Lightly tap the
back of the blade with a small hammer, driving the blade a scant 1/32
of an inch into the seam.  Repeat this operation on all four surfaces.

In some cases this is all that is required, as the glue joint is
usually ready to let go from the long time shear effect of the
retaining clamp.  If not, repeat the above operation, this time going
a little deeper with the blade.  Carefully observe and correct for
any deflection of the blade travel from the plane of the glue joint.
A little practice and you will have a good feel for the technique.
Splinters and splits will occur now and then, but they can be repaired
by gluing the splinters and splits.

After separating at the pouch line, the mating surfaces should be
carefully hand sanded as above.  As with any other restoration
operation, remove as little material as possible.  It is not necessary
to eliminate all tiny voids, as these will not have any effect when
the parts are glued back together and the valve resealed.

Bob Hunt
Kennebunk, Maine