Just stick with your S2 calipers on brackets (£40 off Clint on Turbosport)
these mount your calipers slightly further outboard on the discs than 2 or 4 w/d cossie calipers sit/therefore giving greater resistance to the rotational forces on 285mm discs ie better brakes!
Then put you cossie calipers on Ebay/should get 50 quid for them/and enjoy
the new found tenner at your local Beer vendor.
The above system bolts straight on, no machining and no spacers to worry about/loose every time you dismantle them.
Although you won't be able to 'astound' your mates in the pub with tales
of your cossie calipers...Yawn!