[Closed] can you fit a rear disc caliper to the front end?

most calipers are identical, just the mount and hose length that changes.

Were IS mount callipers different to post mount or just the bracketry?

in what way does the mount change apart from visual differences?

I have exactly the same calipers and adapters front and rear (IS mounts on frame and fork). If you have standard IS mounts then you need a 20mm bigger disc on the front if doing that, as the front standard has the mounts 10mm further from the axle.

IS mount calipers weren't technically different front and rear. But they came in sizes for 140mm disc and 160mm disc which became known as front and rear.

IS calipers are different, looking at the old Deore M555s that came with my old enduro.
PM Shimano calipers (and probably most others) are the same and its just down to the bracketry.