Iron heads at around 9.5:1 are pretty close to detonation on the street in my experience.
(That's with a reasonable cam that isn't bleeding off CR (and low-end torque).
If it doesn't have to look OEM, I'd run aluminum heads, which are better pretty much everywhere you compare.
Paint them & the intake engine color and most folks won't catch it.
It also never hurts to take some nose weight off a car.