Somebody said the "302" heads aren't legal on that motor. Have you checked that out? I have no idea, but maybe the blueprint spec sheet in the NHRA site might tell. Worth looking into, if you haven't.
AFAIK, the 302s are legal for this engine. I've had some contact with Chris Barnes (Mopar Max, Wagons Of Steel, A/SA racer) and he has told me that these heads are indeed legal. He was putting a 2bbl 273 together for a '66 Belvedere and planned to use 302s. He was actually the guy that told me about the Bushmaker's car, he posted a photo of it on Mopar Max earlier this year and we exchanged a few emails about it.
The valves are small in the 302s, I think the same size as the original '65 273 castings so they offer no real performance gain in terms of volume. Not sure of that, but as I understand it, the real advantage of these heads is the swirl port chamber. Of course I could be wrong. I'd definitely double check with the NHRA before I actually put an engine together.
