Matt, the rear uprights are resin ones contributed to the cause by Mark. I'm not sure where he got them from but, thank you Mark!
The rear inboard brakes are steel washers that were soldered into the rear structure for strength. The glued on callipers were leftovers from on old Revell model kit of a Porsche 935 that I built up as a slot car many years ago. I never throw anything away!