Player piano hammers are no different than other piano hammers.  If the
piano, for whatever reason does not play properly, the chances are its
performance as a a player is also diminished.

I see two possibilities for your Weber Grand Pianola, both involve
getting a qualified piano technician who has experience in diagnosing
touch weight problems.

The hammers can be replaced with a a new set of the proper dimensions
and weight, or the hammers on the instrument can be reduced in weight
by tapering and shaping.

Remember, there are several common problems that can lead to "heavy
touch" -- improper hammers are just one.  There is often friction in
action centers and contact points or action geometry issues that will
have adverse effects on touch.  What are the knuckles like?  Typically,
on a player that has gone through one set of hammers, the original 
knuckles are flat and dead.

Get someone who will find the actual problem, not treat the symptoms.
Replacing hammers and related work (touchweight diagnosis, voicing,
etc.) is really not for the do-it-yourselfer -- it takes years of study
and practice.

Jurgen Goering - Piano Forte Supply
http://www.pianofortesupply.com/