Maybe the reason the brakes worked better on yours was because the brakes that you replaced were worn or glazed. That could make a huge difference. From the comparison that I did with the sammy calipers, the piston size is exactly the same. Even the pad size is the same.

I might get a chance to drop in those 5.83s
before Friday when we leave, if I do I'll get
a comparison photo, not the piston out but
the housing size from outside, I'd swear the
new ones I got are bigger, at least the bulge
in the caliper looked bigger.

I received my LWB front calipers a couple of days ago. Piston diameter measures 53.5mm +/- a bit of rust, FSM says 48.1mm for stock swb.

Hi team,
The 4 doors have slightly larger pistons, the calipers are wider ( to compensate for a wider disk ). The disk diameter is the same from memory. The brake booster is also larger.
Here in NZ we get a factory SWB V6, fitted with the BIG brake set up and they stop real good.
I have fitted the vented set up onto Zeuszuki and it all bolted onto Sammie mounts Ok. The Kick calipers have the bleed nipples in a different place so I bleed them off the mounts (used a remote disk for the pads to bite into ). The Kick calipers are also alloy and not cast like the Sammies. The rears - well there is another story in itself

When I compared the calipers from Silver(90 2 door) with the calipers from the kick(92 4 door) the kick's calipers are most definately larger in the body and have a wider spread. I can compare the pistons thursday when I pull one...