I came across this entry on Guitarsite and thought it was worth posting as a reference...
How Old Is My Armstrong? Posted by Kyle Toucher on Sat, 12/07/2002
I have what I think is either a 68 or 69 Armstrong, Serial A339D. Anyone know the exact year of manufacture? Also, I need a the pickguard replaced as it was destroyed at a gig eons ago. Anyone know where I might find one? Cheers.