I thought that might be the case Dan but so far in testing it seems fine. It is the way a lot of turrets seem to clamp tools, certainly the way the Churhill 4/10's, that a friend has, do it.
If using the bolts the other way I would be concerned they would damage the turret slot (its probably only mild steel) thus making it hard to accurately seat tools upside down.
I may have to use shims although the slots seats should, if plans work out
, be exactly 20mm below/above centre. As you know however tools are not that precise especially with standard tips so maybe a thin shim will be needed on some, time will tell.
My last workshop was a GRP cabin and in the summer was very hot and winter very cold, it suffered from a lot of condensation and things got a lot of surface rust but this workshop seems to be a bit better, the coolant seems to leave a film on the ways etc and dont have much of a problem with rust. As you say pollution may well be the contributing factor more than the salt for you, fortunately I am in an area where the air is quite clean