One more thing, but I don't know if it applies to the 600.
The threads in the head of my gen1 run deeper than the bolt. There are more good threads down there, but not many.
I fashioned a longer bolt using a few nuts, red loctite, and a file, that looked very much like the original, and I used that. (It's important to note that I didn't loctite the bolt into the head; I used the loctite to secure a nut partway down the bolt to tighten against the head. I'll have it apart again in about 800 miles to see how it's done.) I had to file the corners off the nuts so they'd fit through the top of the head cover.
I swear the threads was almost gone already as it gave out around 30 in-lbs; another bolt had been "repaired" by the PO, but that repair is not happy. It's some kind of insert, but the insert is stuck to the bolt, not the head. I'll see how long I can keep it, but God help me when it fails. I don't know what I'll do. Double helicoil? *shudder* If I could find someone with the skill to fill it and retap it, that'd be awesome. I didn't even know that was possible. Must be hard to get right.
I now torque those cover bolts to HALF of what Clymers says they should be. No leaks, and they haven't rattled loose yet.