'74 Duster suspension suggestions

qwk dust, welcome aboard. I don't have any racing experience but I have seen the coil spring shocks, they are there to raise up the rear due to sagging leafs just like air shocks, but the problem is that the shock mounts are not designed to take the weight of the car an will eventually rip out of the trunk. With that said, I would go with the XHD springs and forget about biased leafs, after all we're not talking 750+HP, and you are more likely to have wheel spin issues than transferring so much weight that it rolls the car that bad.

BTW where in ORL are you? I'm about 5 min from the track at 50 and 408