This is off the M14 Firing Line Public Forum. The link if you want to read the whole thread: http://www.m14firinglineforum.com/upload/showthread.php?t=42473
The important text if you're in a hurry:
Works like a charm. Install bolt as usual. Put the guts in the bolt and lower the whole thing against the 30-06 case. Insert the extractor tail from above and tap into place with a wodden mallet or screwdriver handle.
To remove guts, lower bolt against 30-06 case and tap out the extractor from below (magazine out, of course).
I now keep a 30-06 case in the buttstock storage area.
Sounds like a neat trick. The rim and base of the 7.62X51 (308 Win.) and the 30.06 (7.62X63) are similar enough and the added case length of the 30.06 means the base of the case protruces out of the 308 chamber and allows you to install the extractor pretty easy. You do have to make sure the ejector is turned correctly so the extractor can slip down by it to lock it in.