Bigger exhaust piping and or dual conversion. Get a 2 barrel on it at least and make sure you get a good advance curve set up in the distributor. An electronic ignition conversion is a good idea as well.
This ^^^^^^ You might also want to check in over at slantsix.org and do some searching. Lots of good info about increasing the torque to get that brick moving and keeping up at highway speeds. You won't be able in use even an A Body 833OD without mods to support the transmission (what you have is mounted from above with the transmission mount built into the transmission!) and the driveshaft is liable to be less than a foot long (or shorter)!
