Cheers guys, separates it is. Separates feel like a better solution which is why I started out with that in mind.

I must admit I was wondering about the best way to mount the induction switches. The obvious method is to have them directly approach a metal plate as that feels like it would give the clearest detection but it would also be crash prone if the axis didn't stop fast enough. This badly drawn picture shows what I mean (I failed art).
Click image for larger version. 

Name:	sensor arrangement.png 
Views:	898 
Size:	10.2 KB 
ID:	10874

My concern with the non-crashing arrangement is that the sensor won't have a repeatable home location.

Update... I see Jazz has just posted while I was writing this, that looks like a vote for the non-crashing arrangement with a very small gap.