The 71-74 E-body plug kits are a universal kit that is supposed to fit Cudas and Challengers. You are going to find a lot of differences in those plugs and the ones that were originally on your 73.
I bought that kit too. I have a bunch of plugs left over. That kit comes with (8) large plugs. (4) of one style and (4) of another style. My 73 used just one style of plug for all (8) large holes. I think all the smaller holes were originally filled with rubber plugs. The kit doesn't give you enough rubber plugs to fill all those holes. Right now, I have the plastic plugs in the trunk right behind the rear seat. I think I'm going to clean up a couple of the original plugs to reinstall there though.
The kit also does NOT include the plastic plug for the windshield washer manual foot pump.(if your car came with electric washers) I had to reuse my original plug. Also, I don't know how you are supposed to install some of the other plugs.(fuel gauge wire, speedo cable exc...) My new wiring harnesses came with those plugs already installed though so I don't have to worry about it.
The only plastic plugs that I know for certain came on 73's are the very small ones at the bottom of the truck lid, the odd sized one for the manual foot pump and the ovaled one on the firewall. Let me know if you need any pictures.