Thanks for that idea. I've spent an hour or two looking at ways to make such an angled system, but concluded that it's too tricky. I think I will give the back to back option a try, but as a "face to face" configuration, with the rails fitted either side.

The rails will be fitted inside a fabricated channel section, capped at top and bottom to stiffen it up. The slides will be bolted either side of the "tongue" of a hefty bit of T section, which in turn will be bolted to the carriage.

The advantages this arrangement has is that it's relatively easy to make and align, plus it's quite narrow, which gives a smidgen more useful travel.

I will try and post a sketch later.

Jeremy