In regards to the left and right head.
EGR is one issue, just plug as you mentioned.
I have a set of Apache heads and are L & R.
It is the oil drain-back holes that you need to look for, I am guessing that the 5.7 are the same as well. But check to make sure. I have circled where the oil hole is, as you can see because of this they are not interchangeable. I believe the hole can be drilled as there is material there to make a hole.
Also on these heads the exhaust manifold holes are drilled differently but can easily be drilled and taped as there is plenty of material there as well.
Just check your 5.7 heads to make sure all is OK with the oil drain-back.
Let us know what you find.
I have 5.7 but it is still sitting on a shelf.