Mine are similar , if not the same year. I used angle iron, 1/8" thick steel. I'd suggest steel over aluminum as it is 3x stiffer so the lights will not vibrate as mentioned above.

http://i843.photobucket.com/albums/...ogress/Exterior%20Completed/2a66a695.jpg


'69 1/2T stepside, Sea Foam Green, 250 L6 w/ 3 on the tree, not an option on it, in the family since new.