An adjustable upper control arm is recommended to fix the pinion angle - it also helps significantly with wheel hop. Most people, including myself, go with relocation brackets for the lowers (and non-adjustable Aftermarket lower control arms). Also, remember to get an adjustable panhard bar to re-center the rear axle and to get an alignment once everything is complete and settled. Ideally, shocks/struts would be replaced as well. This is dependent on how stiff the new springs are and how low you plan to go - 1.5" drop is sort of a grey area of whether shocks and struts are needed. It can go either way. Some people have no problems and some people do. I would recommend BMR for just about all of these parts (although i use Steeda springs). To do it right, lowering a car takes much more than just lowering springs.
2013 Mustang GT w/ Track Pack - Steeda Ultralite Springs, Koni Str.t Struts/Shocks, BMR LCA & Relocation Brackets, BMR Adjustable UCA and Bracket, BMR Adjustable Panhard, DSS Aluminum Driveshaft, Bassani x-pipe and catback, MGW shifter, JLT CAI, Steeda Tune