Re:
They actually go uo to Mark 5 now for 175mm axles (the "marks" are literally tally lines engraved on the rod, so a Nark 5 has 5 marks).
Older hubs can use two-piece indicators which screw together inside the hub and give the adjustment indication at the LH end of the axle. These can be a bit of a pain but some (e.g. the AM indicator) can be swapped for a common AW one-piece toggle if you fit an AW clutch key,
