Typically the longer stems are used with full wheel covers, and the shorter ones with trim rings. I have original wheels w/ NOS wheel covers and a set of GM rally wheels, so I had to get 2 different stem lengths.
Here is a CRG thread showing the shorter length valve stems on unmolested rally wheels:
http://www.camaros.org/forum/index.php?topic=9824.0
Now, do you have the correct old style 'winged' wheel weights? These cal also be seen the the photos on CRG. Then you have to figure out where to get air from 1969. It just keeps on going...