When I restored my Ampico B, I made gaskets for the unit valves out of
1/8" polyethylene sponge.  This stuff is very durable and will conform
to uneven surfaces.  It has some memory if not squeezed hard enough to
break the closed foam cells.

It can be had in self adhesive versions with a very strong adhesive
which is a little difficult to remove.  The un-coated material can be
lightly glued just to keep it in place for assembly.  I have removed and
replaced valves without leaks but would recommend gasket replacement
whenever a valve is replaced.

I made a steel rule die for the B configuration.  I am not sure if
this will work for the A too.  I think the only difference is that the
B version has a large enough hole to vent the ball bleed.  My die is
quite sloppy as I am not a die maker.  If someone wants to borrow it,
they are welcome but it is a bit fussy to use.

The sponge is so easy to cut that it would probably make more sense
to use a metal template and x-acto knife if making just a set or two.
That is what I should have done instead of spending hours making
a marginally useable die.

Best regards,
Spencer Chase