Not saying it is impossible but 286 on the exhaust at 28" is absolutely phenominal, you could sell that port design to Chapman for their CNC program and make a fortune!! I have never seen or heard of a S2 exhaust flowing that kind of number, especially at .650
I have found the best flowing heads come from Busch engines, Moroso ported heads(dont know who actually did their work) are the best flowing at all valve lifts (stamped BGN followed by a #)
next are the Busch heads by Howe (as stamped on the end) and also another excellent head is the ones ported by Holmes&Eames (stamped H&E). Find any of these 3 and you'll have a winner.
Bill