I have 10 inch brakes on my 74 duster can I take a setup of 9 inch brakes off a 70 dart will it work and what do I need to do to make it work. Wanting the 9 inch on my duster

I believe you would bolt on the 9" spindles & everything outward from there with the 9" setup. The only thing different I could think of is the 70 spindles would have the small upper hole for the early UBJ & not sure if the 74 10" spindles would have the small or the large hole. If the 74 spindle has the small hole it is a bolt in & if it has the large hole Doctor Diff has a sleeve to make up the difference between the smaller tapered ball joint and the larger 74 tapered spindle upper hole. iirc it is a match (both have early small ubj/therefore sleeve not needed

Both '73-up drum and disc used the same upper A with the large upper BJ.

The OP wants to put pre '73 A-body brakes on a '74 A-body.

In this case, he must also install pre '73 A-body upper control arms (small upper ball joints), lower ball joints and lower ball joint bolts.