I don't know for sure but I think in 73 the slotted mags, hubcaps with trim rings and some hubcaps. I don't think the magnums were an option in 73. The slotted aluminum mags took their place. I'm no expert so I could be wrong. Ryan.
Mag 500's were not an option in 73. The ONLY wheel option was the aluminum slotted mag. All other options where wheel covers aka hub caps.
Personally OI think they mad a mistake not having the Mag 500's in 73. But at the time the Aluminum Mags where a big thing and people were taking thier 500's off and buying the aluminum wheels.
Think about it. it was also the time of leisure suits and 2" heels for men!!!