http://www.usatoday.com/news/bushdocs/10-2_2000_Personnel_File.pdf
see page 16 of these official docs...zip is 77034
I checked out the documents at "Miscellaneous". The ones with the 34567 box address and zip code 77034 are dated: 1 Dec 69 and 9 Dec 68.
A document further up the page is dated 11 Jan 71...it doesn't have a p o box, but shows a zip code of 77030.
It may not mean anything...maybe there were two zip codes for the base. But perhaps the 77034 zip code was no longer operative in 1971.