I've seen on this board that a popular mod back in the day was to use cadillac tail lights - the long vertical shape fits nicely into the big fender.
Heres a sample
http://67-72chevytrucks.com/vboard/a...1&d=1315018631
And here's a post about it
http://67-72chevytrucks.com/vboard/s...d.php?t=556774