RGS/SFC had PS14 M/Cs as standard, these obviously have a 14mm piston.
I am aware of Brembo PS17 M/Cs having been widely used in racing, but never in a road application. This would result in pretty lousy brake performance with enormous effort required at the lever together with the standard P08 calipers. Might just work out with P09s or four/six pot calipers though.
While seals for PS14 and 15 are readily available, I have no idea if seal kits are still available for the PS17 at all, Brembo have discontinued several variants of their kits.
piet