Sw20 rear caliper info

Are the mounting holes same size and spacing?
Yes.

Is the clearance from mount to "bridge" the same, ie the distance from mount to outer diameter of disk?
The rotor for the 16v calipers is 262 mm diam, and the rotor for the 22v calipers is 280 mm diam,  so I'm not sure about that one.  I believe the pads are the same for both 16v and 22v.

I don't know about the piston size.
 
I hope that helps.

Adrian, I just had a look at a couple of calipers.
Without disassembling them, the pistons 'appear' to be the same for 22v and 16v, but don't quote me on that.
 
The 22v mounting bracket is different, locating the caliper housing about 9-10 mm further out from the hub center that seems logical going by the larger diameter of the rotors.
 
However the 22v caliper casting is much larger and while the inner edges of the two appear to be the same offset, the outside edge of the 22v appears to be moved out by the 6 mm extra thickness of the rotor.
 
I do not have a 22v rotor to check, but apart from being a larger diameter I would suspect that the inside edge would be the same offset as the 16v rotor.
 
This all gets a bit complicated but that's the best I can describe it so I hope it helps.

So that would imply that the 16mm caliper assembly (including the mount) would bolt up approx. 10 mm closer to the axle.
Are the mounts similar apart from the spacing from the axle, eg does it look like a 16mm caliper body would bolt to a 22v mount?

I am trying to work out if I can use zzw30 rear disks, as the offset looks perfect (no spacers), and 16 mm is plenty of thickness for an aw11 rear.

I agree about not reinventing the wheel, but to be strictly legal in vic. means I can't go 22v + aw11 front disk + 6mm spacer.
The other easy swap involves 22v + modified renalt disk + hub ring.
It is probably a forlorn hope, but I thought I would look at 16mm otions, partly because I think 22mm is a bit overkill for the rear.
Thanks for your info.