This was a post I made a while back that may help. They attach with a sheet metal screw on one side (you can see the hole in the dash) the other side attaches with a clip they either than face straight down for hose attachment or they turn into the firewall some have two screws for attachment and no clip but they pivot for ease of attachment one side has a full hole the other a slot.
Two styles of 1954 vents both made of aluminium one type straight the other reverse bend see pictures:
http://good-times.webshots.com/photo/2586236450102454676qRPcYh
http://good-times.webshots.com/photo/2021907660102454676cpkuJb
Next there are at least two styles of sheet ducts: 47-51 style:
http://good-times.webshots.com/photo/2405252410102454676ppisPX
52-53 1/2 ducts:
http://good-times.webshots.com/photo/2809720060102454676gVgVNT
http://good-times.webshots.com/photo/2653102730102454676PXUNwF
Then to add even more confusion I have seen them with and without these black spacers (usually on 1947-1950 trucks).
http://good-times.webshots.com/photo/2661175600102454676CudWvK
http://good-times.webshots.com/photo/2246331650102454676MRFRlr
The driver side kicking right a bit depending on the style.
_________________________
1950 Chevrolet 3/4-Ton 3600

http://community.webshots.com/user/RugerWSM?vhost=community

Last edited by Brad Allen; 07/19/2010 8:15 PM.
1950 Chevrolet 3/4-Ton 3600
More pictures on Flickr