I measured one and they stick out about 6.0 cm from the disc surface. Also be aware the FRS discs are thicker (28mm) than the standard Cosworth discs (24mm) and also have a lower height (52.7mm) than Cosworth discs (55.1mm) which makes the caliper stick out even further.

So I think you should have at least 6.7 cm room from the standard disc surface (6.0 cm + 0.4 cm thicker disc + 0.24 cm less heigt). And of course a few mm clearance.