I just went out to measure an eagle head. No shim I got 2.015. It came with .040 shim. I have a few .080 shims on the peg board so they must have made a change somewhere. Anyway
2.015-.570=1.445. So I really don't see how you can run a 6.4 spring safely at all

Also CB on the one spring out of this eagle head i just checked was 1.39