In fact, we used to use stale gas back in the '80s before everyone (WKA & IKF) went to alcohol.
OP, as soon as you cut those eyebrows, and valve relieved the head for a bigger lift cam, you lost compression ratio.
You're likely around 6:1 now even with some pop-up and a flat-milled head. There are billet heads that will help some, but the majority of the loss is over the valves.
Keep this low CR (and coil retard) in mind when setting your ignition timing!