I don't remember all the specs, but Back in the '80's I had a 65 Valiant 4 door sdn with a 273/904/8 inch conveter/ 8 3/4 rear. Ran 12.8's about 104 mph. Tried the 360 heads. As someone else stated the loss of compression, offset the better breathing. Times were almost identical. If doing it today, I think I could have been better with the 360 head, as I would have done other work to get a better gain with the 360 head.
PS: The cam I was running was a Crane flat tappet, somewhere around 520 lift.