Re: Wheel cylinders - 15/16ths ? 7/8th's ?
I can't confirm which is the police version, but I can confirm the larger wheel cylinder (or caliper) will apply more pressure to the brakes. In other words the 15/16" bore will give you stronger brakes. The opposite is true for master cylinders, a smaller bore master will give you stronger (more PSI) brakes.
Most Ford wheel cylinders interchange so you can actually use them to dial in your brake bias instead of a proportioning valve if you wanted. The 11/16" wheel cylinder from a mustang and a 1-1/8" wheel cylinder from an f350 dually will swap. If your rear brakes are locking up too soon you can go down a size or two. It takes trial and error but it does work.
I'd guess the police/taxi wheel cylinder is the larger one based off of that, no clue for sure.
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67 Fairlane GT, 390, 4 speed
78 F150 rockcrawler truggy, 351M, 4 speed, 42" tires