Your truck used 19ga metal for its exterior panels. Good luck if you can find it as only a few select suppliers have it.

I would use 18ga and you will want to get CRS or cold rolled steel, its the closest match to the older steel GM used...Eric

Currently working on custom metal and How to videos.

1949 and 1972 chevy trucks
70 chevelle SS455
Pictures of my work and projects
http://community.webshots.com/user/sevt_chevelle