Locking Gas Caps

Determine if your car has the vapor emissions system:

http://www.forabodiesonly.com/mopar/showthread.php?t=183956

What does the original cap look like?

If it's pretty flat with a simple pair of lock tabs and no pressure vacuum valves in the cap, it's "early," no evap emissions

If the cap is deeper, see here

http://www.forabodiesonly.com/mopar/showthread.php?t=194100

you have the evap emissions package.

70 came both ways --if it's a CA car it probably has it.