I have one on my 77, I don't recall where I ordered it from, but it looks exactly like this one.
http://www.x2industries.com/hidden-h...2#.W5KEeehKiUk
You will need an extended hitch to actually use it, like this...
https://www.etrailer.com/Ball-Mounts...tch/80232.html
Robbed a flip down tag bracket from a junkyard Caprice, works great.