Fraser,
The short answer is 'I'm not sure', but want to check. I do like the idea of building my stuff to run on either 32mm or narrow gauge, if it's not too much trouble to do so.
It isn't.
The reduction in flange-track clearance implies to me that the chassis clearances (sideplay) may have to be more carefully thought out. I'm just trying to establish what/whether/how. After all it's possible to build many locos without side play in f/s and they'll go round bends because of the flange-rail clearance. So, if that clearance is reduced, then the sideplay must increase to compensate. Or so my thinking goes.
Most of the time, normal working sideplay is quite sufficient. In fact with trucks/bogies, it's better as there isn't so much slop movement.
That's what I want to check. I'm working on a couple of 4-4-0 locos with very restricted bogie swing, so feel the need to do some quick sketches in CAD and make sure I'm on the right lines. It'd be a bit of a pain to have to take a near-complete chassis apart to remedy a problem with the frame spacers!
Take a trip up the M5 to check
Richard