8 3/4 rearend swap in 70 dart

You probably won't be able to use the brake lines, the vent bolt/block probably isn't in the same place and the 8 3/4" housing is about 1-1/8" wider than a 7.25" housing so the lines would be short. Other than that you already got most of it, shorten the driveshaft, use 8 3/4" shock plates and u-bolts for a 3" diameter axle tube, check the yoke to make sure you can use the same u-joint or if you need a conversion. The parking brake lines should be ok, same for the brake hose coming down to the rear axle but those are usually worth replacing anyway.