[1QuickS]

I don't recall spacer dimensions, I measured all components & machined them at the time I set them up. The idea is to adjust thickness of spacer so disc is centered on the caliper.

I looked at removal of brake mounting tabs and welding/machining new tabs but stayed with 911S calipers. Plenty of braking power & bolt-on convenience. Unless you are using race rubber I doubt you can utilize larger brakes in the rear, especially with a good brake pad compound. I made a dual master cylinder brake pedal box & needed to use two different diameter master cylinders and the balance bar to reduce front braking force to balance it out with the rears. I had alloy 911S front calipers with SWB 911S rear calipers and 205/50 fronts and 225/50 rears. Point being SWB 911S rear calipers have plenty of braking capacity, especially with typical tire sizes/compounds you might use on a SWB chassis.

Changing calipers is more involved than just bolting them on, front-to-rear brake proportioning and pedal effort are affected and need careful review.