Performer RPM Magnum heads?

I have a set on my Magnum 408. Mild cam, pump gas, 3350 pound Dart, 3.55 gears and it runs 11.55 @114. No porting or anything fancy, it's a garage built street car. No Dyno sheets or anything unfortunately.

I had EQ heads on a 360 Magnum in the same car. It ran 12.60s. Same cam, similar compression, same trans/gear/tire, etc.