someone said yesterday that they saw this same address on docs from Bush to the ANG. Not sure if it was true, but it was allegedly checked out and found to be correct.
After a great deal of research, I don't believe that the PO box is false. The same PO Box number appears on several other original documents in Bush's military record file, and the authenticity of these documents is not in question. What may be unusual in the Killian "memo" (besides the proportional font and anachronistic characters) is the choice of address - any such correspondence would likely have been on letterhead of the parent organization (the 147th FIG, rather then the 111th FIS).
No way a unit would have a post office box when they were stationed at Ellington. The box may have been real but no way that was the address of the squadron. I would like to see any documents he sent the squadron with that address. AF would never have paid for a post office box and can assure you that the post office wouldn't have given them one in a different zip code area to boot.