Before you decide on the heads I would CC a chamber in each heads, that way you will know exactly what your compression ratio can be and not hope it is near stock on the combustion chambers scope twocents
I've CC a ton of both X.J,U,O and other stock 340 heads, none of them where larger 67.0 CC shruggy work
I haven't seen a flow sheet on a OEM stock iron 340 head in a lot of years no I have no way to judge the new Eddy aluminum heads are any better or worse than the original iron ones are shruggy

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)