Which heads?

If I was to use magnum heads, I would just put the whole magnum motor in the car. I have a pair of good 318 heads on the car and a good pair of 308's on the bench. I know there is gain going either way, but I'm trying to reach high 13's on a very mild 318. Every tenth counts, that is why I'm interested in different perspectives. Keep in mind, I'm using manifolds instead of headers, and that will help low end torque if I was to use the 308