In many, if not most, player pianos made in Europe are lead weights to
keep piano keys from dropping as the player mechanism works. Balancing
keys is something of an art but just remove the lead weights so the
keys can drop.

If you want to go to trouble of balancing the keys for hand playing
then do so, but my guess is the weights you removed will not make an
old upright play any better by hand.

Don Teach
Shreveport, Louisiana