Going to a closed chamber head from a stock smogger head will bump the compression up quite a bit, I could see those numbers being real.

I used to have a dish piston worn out 360 shortblock under a set of ported X heads that made 310HP to the tires on a chassis dyno and that was with a 3800 stall converter chewing up some dyno numbers. It ran 12.72 in my 3500lbs Barracuda.