13s and 15mpg Magnum head 360

I am running the XE268H cam in my magnum headed 360 in my 68 Barracuda and it's run a best of 13.7 @ 102 and I get between 14 and 15 mpg around town. I have used a 600 Holley, 725 Demon and a 750 Holley, all vacuum secondary carbs. The 1/4 times and mileage numbers are with the 600 Holley. The engine runns better above 5500 rpm with the 725 or 750 but the throttle response below 2000 is so much better with the 600 that I usually use the 600. The Holley 750 is very close to the 600 and the 725 Demon is just not happy below 1500 rpm. I am using a Crosswind manifold and headers.

My heads cc'd at 64 and it's easy to measure. A graduated syringe from the pharmacy for a couple of bucks and a piece of plexi glass is all that's needed.

The two mopar performance springs require 2.2 retainers. I am using the RT spring which is good for .525 lift and was recommended by Comp when I selected the XE268H cam. Comp now has a beehive spring for the magnum heads but don't know if it works with the stock retainer. The stock rockers work fine with the aggressive XE268H cam.

I have KB107 pistons with the block machined for zero deck with these pistons. With an 0.039 head gasket I have 10.6:1 compression.