Now that Eliyahu Shahar has listed more information about his piano,
I would like to submit my theory on the missing parts.  Typically a
1923 Knabe Ampico would have an expression cutout and a pump reservoir.
Most often the cutout is mounted on the bottom of the primary valve
chest.  There will be no screw holes in the piano itself.

The same situation applies to the reservoir.  It is typically mounted
on the pump.  The mounting brackets are on the top of the pump, and
out of view.  Again, no screw holes in the piano.  A peek at the pump
distribution block should reveal two 5/8 inch outlets for the
reservoir.  Again, these are on top and out of view.

The equalizers are sometimes omitted from a piano, and I have seen
Knabes from 1923 that did not have equalizers.  Look very carefully
for screw eyes.  These are the equalizer spring attach points.

Finally, if the parts installed in this piano are not original, there
may be no evidence at all.  Some smaller pianos had the pump reservoir
located some distance from the pump.  If your pump came from one of
those pianos, then there will be no mounting brackets screw holes on
the pump.  Likewise with the primary valve chest.  If it is not
original, the tell-tale screw holes there might also be missing.

I strongly believe that your 1923 Knabe originally had a pump reservoir
and an expression cutout.  More than likely, the last rebuilder removed
them to save time.

A word about your valves.  The part that you can see that is turning
to dust is the outside surface.  The inside valve, being protected,
will be less deteriorated and still functional.  If the outside leather
is rotten, the inside leather is not far behind.  You should rebuild
the valves.

The primary valves on your piano may be different.  The outside portion
(the acorn) may be a molded piece of Bakelite with the leather seat
being glued to the chest top -- not the acorn.  Many of the Bakelite
pieces will break upon removal.  I have spares if you need them.

Bob Taylor