That piston size is very close to the stock and XP8 piston sizes, about 45mm.
I had OEM 65-82 Corvette calipers on mine first, those are 48mm(1.875") pistons. That was a little extra brake power over stock, enough to lock the brakes at 80mph. Currently I have 43mm SSBC calipers, these are little less powerful than stock. I think a piston size around 45mm is ideal, shoot for that if you have choices.
It does look like someone(maybe even Baer) put together that set of parts. It may be a great combination for many wheels, obviously 17" at least. But the clearance behind each wheel is different. Set those rotors up on the hub again and see what space there is at the tie rod end.
If you do have to have new brackets made(you got to do steel for safety), why not alter the rotor offset as part of the dimensions of the bracket? I'd suggest aiming for the stock clearance to the tie rod ends.
I do have two extra pairs of rotor hats. I had three pairs custom made, the costs are very high for one pair. I would bet that you can build a rotor by using a pair of my hats. The rotor discs are not the expensive part, the hats are. You can buy the rotor dics from Coleman for $150 to $200 a pair. I'm talking about any dimensions, 14"x1.375" etc, or the 13"x1.10" you have there.