Robin: You have nicely pulled together info from various posts to make a good addition to FAQ's. Hopefully it saves a few original screw heads. A link to Galazan's might be useful for those times when screws are so badly damaged they need to be replaced. They sell a set of Parker action screws for $35. They need to be final fitted as the heads are extra long.
http://www.csmcspecials.com/SearchResults.asp?Cat=19
Cheers
Jack