Cylinder head discussion 340 with stock above deck pistons

As far as the original question with out going to far off track. Aluminum heads are definitely better. Lighter and usually flow better with probably a little more compression. As far as everything else I couldn’t say. One thing I do know is that the cam your running isn’t fully utilizing
Maybe an xe284h would be a better cam, would have to cut the guides a beleive if it went in the stock j heads. But I would also probably need to go with 3.73 or 3.9 gears out back if I jump the cam up much