need help with 8 3/4 drum breaks

I'm no expert, but you are gonna need to post a little more info and perhaps add some pics of the hardware before anyone can offer any help.

If the 8 3/4 was not original on the car and you went to a "chain" parts store where they look everything up on the computer, my guess is that they sold you a rebuild kit that fits your model year but not the 8 3/4.

I'm not 100% certain, but 8 3/4 were small bolt pattern only and were not available after 72. Pretty sure that's true for darts but don't know about dusters demons etc.