I have 3 sets of Boxster S/996 rear calipers lying about... 
I assume you mean RS2 to S2 carriers as S2's calipers just bolt on... Did you have to modify the mount?
What size discs from which Seat? do the disc hats match the golf ones?? Assume you are still using MK2 4 x 100 hubs?
I was looking at getting them to fit under 15" RA's & RM's (Just bought a set of RM from Germany)...
A M8 of mine machines up brackets for S2's to mount Boxster S 996 Front calipers he does two sizes one for 16" alloys and one for Min 17" so could get hime to make up a bracket... just need to sort some suitable discs..
Carrier bolt holes end to end is 13cm as long as they match the carriers your calipers are fine!
Yes the rears are the ones I went for that fit over the 28mm width discs, but I had to machine 3mm off the bolt retainers to the pads they didn't clear, but 3mm is nothing you can mod it in ten minutes of even grinding.
305mmx28x4x100 hat 38mm
Yeah Carriers RS2 Part 8A0615125A
Discs 6KL 615 301 Seat, that’s a 12"-304 mm diameter
4 X 100 Seat Ibiza Cupra R 1,8 turbo on old platform ('00-'02 ) Seat Ibiza Cupra R
Thats it But I did order new caliper bolts from Porsche direct it was cheap just to be sure.
This only applies to later 16V models with the bigger discs by the way as mine was on the G60 hubs set up.
You could go down MK1 TT brakes @ 310mm discs, but they are massive and heavy pointless to the power to brake ratio IMO.