Non-destructive removal desirable

Someone gifted me a Tri-Ang Southern Railway utility/CCT van (bogies and corridor version).

One of the bogies swings freely, the other is a bit more stiff. At minimum I'd like to know how I might loosen it up, if at all possible.

I'd also like to know if it would be possible to remove the bogies with little to no damage to the rivets. I know that heating with a soldering iron can be good for removing metal pins from toys, so would heating the rivets do the same for them? I mean to repaint the van, so it would be ideal if I could get the bogies out of the way, and if I could do so without damaging the rivets that would be perfect.

Firstly, if it's just dirt/muck/fluff restricting the bogies swing, then washing it, first withwarm, soapy water, should help. Next wash with IPA of meths (wood alcohol).

The simple answer to rivet removal is NO, don't try heat, you'll melt/distort either the
plastic floor or the bogies before the rivet. If you really need to remove them, rather 
than just mask them, you will have to drill them out (carefully, because of the heat)
or 'unfold' the riveted bit, and replace with a suitable bolt and Nyloc nut.