1973 340, want more power.

Hold on to your horses, from what I can gather, you have a 340 with an 8 3/4 rear in a 74 Duster. What a great combination! Before you do anything, tune that thing to the max. If there is a hint of miss anywhere up to 6,000 rpm, get new high quality cap, rotor, platinum plugs, and Taylor Spiro Pro wires. Gap the reluctor to factory spec and set timing to 10 degrees BTDC. Next if you have highway gears, 2.76 or 2.94, we used to run 3.23 for a daily driver cruising at 70 mph all day long. If you are not on the highway much try 3.91s. Get rid of the Holley and get a Quadrajet or a TQ. Make sure your carb opens all the way when you mash the pedal. Factory air cleaners are as good as anything, don't waste your time or money. Try to do one thing at a time, so you know what works and what does not. Since you have an 8 3/4 rear you can get the whole center section and swap them back and forth. And yes, get a Sure Grip.