he has the springs, with the two-point arms. ( I know, had a 66 once, now have a 64 ) So.. you're not going to need traction bars, or pinion snubber, cause those are band-aids for leaf spring setups.

One mod you can make, is to get a one-piece driveshaft fabbed up. By eliminating the center U joint, you can net a tad more power to the rear.

You can drop a pozi unit into the rear end, and that'll help you get off the line. However, pozi units do have their drawbacks. I had a clutch type limited slip put in my 78 firebird, thought it would solve a particular problem I was having: the car would fishtail between gears. Turns out, the limited slip actually made the problem worse. Also, it makes the rear tires wear badly to the inside. SO .. limited slip ( or pozi ) helps you get off the line, helps you get out of the mud, but wears your tires faster and makes you fishtial harder. Although, you'll have little worry of that lead sled fishtailing.

You could try to loose some weight: ditch the tailgate, spare tire, and bumper jack.

Fine tune the ignition timing. Fine tune the plug gap. Put in HEI if you don't already have it. Experiment with different jets in your carb. Duct your intake to pick up cool air. Put on some BIG mufflers, then vent it out in front of the rear wheels. I'm running Dynomax turbos on my 64, but they are a tad loud for my taste. The massive flowmasters on my 78 firebird are actually a tad quieter. An exhaust cut-out is pretty fun too.