It was an old school trick. Putting 305 heads on a 350 does give more bottom end torque with higher compression and smaller airflow passages. It should also improve fuel milage. Where the combination suffers is in top-end performance, usually you don't get much above 4,000 rpm. But you also have to look at how much you want to run above 4,000. In a driver it isn't much.
My recommendation is to leave the heads, but put on the q-jet. Properly tuned, it will get you better milage than the 2 bbl.
