I'm away from the computer where I have the documents downloaded, but I can tell you which ones to look at. The Westheimer address is in the 1972 and 1973 military payroll records that Bush released. Longmont is on most of the 1968 documents that the pentagon released.
I think you found an excellent point..though it may have been his parents address also as it is listed in one form in 1968 there are documents in 73 listing the Westheimer address and with further looking I am confident you are correct..
as an aside look at this page 16 for a letterhead including a seal used by the ANG in 1972..obvious the others are forgeries and not written on letterhead..need the originals to check for watermarks..I dont know how to post the letterhed letter..
ANG LETTERHEAD pg 16
http://www.usatoday.com/news/bushdocs/10-2_2000_Personnel_File.pdf
many more doc to search are here:
http://www.usatoday.com/news/2004-02-14-bush-docs.htm