Very true. The First generation Summit 650 and the Third generation Summit S-670/E-670 are very different.
But there is not a lot of difference between a Third generation S-670/E-670 Summit and a Third generation S-650/E-650 Summit other than the S-670/E-670 having the Sear Station burner and the S-650/E-650 not having the Sear Station burner.
I have an NG manifold from a Summit 6 burner serial #EZ460555 and am looking for a LG manifold, im new to this but if they are compatible ill swap with you for your NG manifold