Are you just cleaning it up or trying to lighten it? You certainly don't want to cut down to the ring gear. I just messured a couple out in the garage and got .200" step to the ring gear, I would think you could safely go another .050" from that maybe even to 1/8". I don't have any specs, that is just what sounds good to me.
God Bless.
Tim http://yblockguy.com/
350ci Y-Block FED "Elwood", 301ci Y-Block Unibody LSR "Jake", 312ci Y-Block '58 F-100, 338ci Y-Block powered Model A Tudor
tim@yblockguy.com Visalia, California Just west of the Sequoias