Lucian,  First of all, you didn't ruin the piano because, if you decide
installing the weights was a mistake, you can simply remove them and
fill the holes with wood or a wood substitute.

The key question is, did the weights accomplish your goal of reducing
the heaviness of the action?  If so, you were successful.

The place you chose to install the weights is unconventional, and
I can't image how you could get any but a very small weight in the
restricted area you placed them.  But again, that's not important if
it achieved the effect you wanted.

David Stanwood, RPT, has for many years studied and experimented with
piano action geometry, leverage and weighting, and has come up with a
system that results in a perfectly balanced, even action that is a pure
delight to play; I've tried several pianos with actions redesigned
by his system.  You can find out more about this on his web site,
http://www.stanwoodpiano.com/  I believe his work has been only with
grand pianos, but you may get some ideas about verticals from reading
his material, or you can write to him for advice and suggestions.

Good luck!

Larry Lobel - Virtuoso Piano Service
Petaluma, California