Are you running a road draft tube? The valve covers appear to have the mounting bolts straight across, if so the heads are not stock 265's. All 265's and 283's from 55 to 57 had staggered mounts on the valve covers and they also have no motor mounts on the side, that changed in 58. You won;t be over carbed if you have a fairly stout cam as I ran a 30-30 in a very bored out 55 265 block and it ran the 2-4 setup from a Vette along with a Sheiffer 10lb aluminum flywheel and it would easily grab 7 grand and then some if I kept my foot in it.