Guy has one he says needs a new blued barrel, has "chamber rust". I saw take off SS barrels for $69 in SGN just yesterday. Is it hard to swap? Head space issues?

Ruger will do it !

Im wondering the answer to this question myself as my barrel is pretty shot out...

you'll need an action wrench to fit the front of the Mini's reciever. I'm not sure if anyone makes one, though a good machinest could. Also some good barrel blocks and a good vice.

 It would probably be cheaper to send it to one of the places that work on Mini's for a barrel swap than buying the action wrench. I'd probably call Ruger and get a ballpark price as they may be the cheapest.

 Of course headspace would need to be checked with the new barrel once installed.