Why limit your self to X or J heads? All 340-360 open chamber heads (except 308s) have the same port and chamber size. The only difference will be the X heads will have 2.02 intakes and the rest have 1.88 intakes.
Dave, I was a little torn between a stock/correct looking motor with some internal mods made and one that I did not care if it had the correct heads or not for the year. Just to broaden the search, I will say that I am open to other 340-360 heads as well.