Me thinks the machine shop, flow tester, goof up something on your heads testing them tsk
I've had a bunch of different BB Mopar heads flow from bone stock 906 and 1963 M.W. heads up to several different sets of MCH CNC ported 440-1 and one set of B1 ported by Koffels. the CNC ported 440-1 with 2.250 intake valves flow right at 370 CFM at 28 inches at .700 valve lift on the intakes on a Super Flow 600 bench with a 4.375 bore and the B1 heads on the same bench with the same bore size flowed 420 CFM at .700, 430 CFM at .900 and at 1.00 lift shruggy
If I was you and wanted to learn more I would call Bob at MCH (568-468-7914) and talk to him about your heads. I'm sure Ray Barton did a decent job on your heads but I don't know what you wanted them to accomplish originally work shruggy

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)