72 Duster tail panel on a 73

Should only take the tail light brackets. The later Duster's used a quarter panel brace like this, not sure if the '73 did or not. But the '72 tail light bracket should include a brace, so you'd just remove this one and install the brackets.
duster-to-demon-swap-2-1-jpg.1714974886.jpg

This is on a Demon but the '72 Duster brace is similar in that it is part of the tail light bracket

duster-to-demon-swap-2-3-jpg.1714974888.jpg

The bumper was pretty much the same for '72 and '73, no shock mounts on either so the rest of the tail should be the same, ie, it should have the corner reinforcements for the standard, non-shock bumper that are missing from the rear shock mount bumper cars (74+).

Keep the '72 tail panel on your '73. The '70-'72 look so much better. I plan on replacing the tail panel on my '76 duster with a '71.

There's a lot more to replace if you swap a shock mount bumper car like your '76 to the earlier style. Not only do you need to change the tail panel, but the bumper, brackets, filler etc. Lots more work. There's a how to that covers some of that swap here
Duster to Demon Tail Panel Swap

And here's my '74 to '71 Demon tail panel swap, starts at post #131
My "new" '74 Duster- or why I need a project like a hole in the head

And the bumper swap here
My "new" '74 Duster- or why I need a project like a hole in the head