How to sqeeze out a little more speed?

u need gears to really go faster. i would say 3.90s for your set up, unless you drive it on the hwy a lot. jack the car up on one side only and do the old tried and true test for gear count:

http://www.slantsix.org/forum/viewtopic.php?t=16476&highlight=rear+end+ratio

ditto on the smaller carb...you'll go faster especially on your 60ft times, which are pretty tuff with a stick anyway.
regular shocks in the rear and address the sagging a-body rear end with a re-arch or new springs. pinion snubber if you don't have one.
play with your ignition curve a bit to get about 36* total timing all in by 2K. might vary a little depending on weight and atmospheric conditions...

sb