Umm....the series 2 heads are so absolutely incompatible with your LN3 that it isn't even worth discussing. And you won't find another LIM with the same spacing as the S2.
Your front bank of the engine should tell the story. From left to right, you'll see your exhaust (dictated by the manifold runners), and intake sequence (dictated by spark plugs) go:
Exhaust, Intake, Exhaust, Intake, Intake, Exhaust. Uneven, just like the Buick Grand National.
The Series 2 is EVEN.
You cannot make the heads swap by any means. My suggestion is to get a Gen2 M62 and run the Gen3 2.8" pulley or larger on the setup to begin tuning.