Precision Scale.

  They appear to be Commonwealth lightweight swing motion. Precision scale has 7 foot wb.

http://www.precisionscaleco.com/

 Click on trucks and select HO/ HOn3 and look on the second page.

        Pete

...

They may look gruesome, but they're correct for your road and car...

http://www.20thcenturyhobbies.com/item.php?item_code=BCW-129

As you correctly identified, they also used them on express boxcars.

Replace

You don't say why you want to replace them, but if it's because of terrible rolling qualities -- common among brass cabooses -- may I suggest Intermountain's 40058 ball-bearing wheel sets? The question is whether the IM axle length will work well in the brass frame.

http://www.intermountain-railway.com/ho/hoacc.htm

Replace

Thanks for the responses!  I wasn't clear on why I want to replace them.

I was aware that they are the correct trucks, I'm simply not satisfied with the detail.  I found those Precision Scale trucks some time ago.  They look very nice, and they're otherwise correct in their design, but they're the wrong type of truck (very close, but not the ones).  They're also they the wrong wheel base for the model.  Of course, I'm assuming that the trucks on the model are the correct wheel base.

As it sits, the trucks pivot past the steps by so little that even an increase in 6" to either end would not fit.  I'm starting to wonder if they made the trucks shorter just to make the model functional.  The sideframe casting is pretty thick.

I'll try to chase down those Bethlehem Car Works trucks.  I'd like a better photo to see if they're any nicer looking than the trucks that came with the caboose.

Overland truck on Ebay.

  Hunter.

 Even though it will probably end by the time you see this the seller may still have them.

http://www.ebay.com/itm/HO-BRASS-Overland-UP-High-Speed-Q-Intermediate-Caboose-Trucks-pair-9615-/350498296855?pt=Model_RR_Trains&hash=item519b539417

  Pete

Thanks Pete!

I appreciate that you're looking out for me Pete.  Those look much nicer, but they're not correct.  I'm still following up on a previous lead. In the meantime, I'm going to keep looking. 

I recognize that I might have to settle for the trucks that came with the model.  Like I said above, the stock trucks appear to be correct when I check photos in my collection and online, it's just that the depth of the detail leaves much to be desired. 

I'm not letting this stop the project.  I've been working with Keith at Plano on a replacement for the roof walk.  I should probably replace the steps too; they'll look out of place once the new roof walk goes on.  The antenna on the model is bit too thick and lacks detail, so I'll look for a replacement for it.  The windows will need screens and tracks.  I might add some piping and brake parts because the underside of the model is bare, save or three rough castings of the major air components. I don't typically go all-out on the underside of my models, but I want some piping and mechanicals showing when it's on tracks at eye-level. 

Thanks to everyone who is helping out!

-Hunter