Module idea...

I reckon I should make a movable, pass-through fiddle yard, aka a traverser.

Maybe not this complex:

Maybe something a bit simpler, like this example from Aus:
Picture from David Bromage.

 And another close-up shot from Armchair Modeller Downunder:

The track appears to be soldered on to PCB. The locking mechanism seems to be two standard brass door bolts, with a aluminum plate with holes drilled at the right distances.

I reckon two MMW module plates with draw runners would do the trick. The only question is how long to make it...