I use either a needlenose pliers or small hammer and screwdriver (depending on what's handy at the time) and take my time. I've never caused any damage to the bezels using either method, but there's always that potential. If you have the ability, equipment and material, I imagine it would be trivial to make your own tool for doing this -- just need a handle with the two appropriately spaced "prongs" on the end.
Just found this tool at The Paddock (spurred on by pp's link) that may or may not work:
click here . It's listed for various '64-72 GM stuff but only says '67-72 for the trucks. *shrug* For $12 + S&H, I'll keep doing it the old-fashioned way.
Brent