In my opinion all the 340/360 heads are the same(in the 1.88 intake valve size) now the non mag 308 are claimed to be a slight bit better, head. Mag's all i know about then is that they crack, but sometime will run for a long time that way.
Blocks?????? early ones are said to have a little bit more metal around the cyl walls. Every thing i have said can and will be argued:poke::D