Your flowbench eyeball should be pretty close if they are OOTB heads. On our flowbench the OOTB RPM head is 248 cfm @ .500" lift and 250 cfm @ .600" lift. If they have been ported you already have enough cylinder head to punch into the high 10's. Testing your heads sure wouldn't hurt.
What manifold is really on there? Because Edelbrock doesn't make a Victor Jr for the Chrysler small block RPM heads that I know of. There is the Victor 340/360 and the Super Victor. The Victor 340/360 has 318 size ports and would need some extensive work to bring your engine to it's full potential. A ported set of RPM heads and a small mid-range solid roller should go into the middle 10's with a 416 stroker.
