I remember a discussion a few weeks ago about end blocks, so I thought I would throw my (late!) 2 cents in.
There was some discussion over whether the blocks should attach to the top and back, if this would dampen movement of the top/back, etc.
I have been using an end block that I think is a fair compromise (minimal attachment to the top and back, and still thick enough to take an end pin or jack).
Like some of you, I have been using baltic birch ply for the endblock, so what I am doing is to coutour one side to fit the bottom curvature of the sides, and then marking off an area that is the same width as the kerfing you are using. After doing this, i chamfer the rest of the ply block with a 25 degree chamfer bit, so it will not contact the back and sides.
This is easier to show in pictures than in words, so here are a couple of pics:
Curvature of guitar bottom sanded into end block
Chamfering of the rest of the block, leaving a ledge for top/back/kerfing to glue to.
Just another take on it...there are as many wasy to do things are there are guitar builders, I think! :)