Made this from some threshold plate and some 20 x 20 alum square bar. The weight will attach to the adjustable slider block to achieve balance point. Screwed into existing holes in the OTA.
Baz.
http://i19.tinypic.com/673wra9.jpg
http://i18.tinypic.com/5xep8iq.jpg
http://i18.tinypic.com/6f5zdph.jpg
http://i15.tinypic.com/4t87ntz.jpg