2 Rail wheel sets

To provide a good answer it would help to know more about the models and, specifically, the trucks.  It would help if you know the brand of trucks we're dealing with here.

Jay

NWSL should have what you need otherwise there are people with atlas 2 rail trucks for sale

Jay C posted:

To provide a good answer it would help to know more about the models and, specifically the trucks.  It would help if you know the brand of trucks we're dealing with here.

Jay

Yes. ID of brand of truck really matters.  There are several sources of wheelsets, but none fit in all trucks - no universal generic...

Athearn trucks and the Weaver Delrin trucks use the same size wheelsets - Athearn will work which means the Intermountain metal wheelsets also work

Atlas O has their own (as most toy makers do) and even some of theirs use different axles.   Theirs tend to be the longest axles.   They sell wheelsets to fit.

You can use AThearn  or IM wheelsets in many MTH and Lionel trucks - some are a little sloppy fit but still work.   

NWSL has most variety of wheelsets/axles available.

Trucks that can accommodate 3 rail wheels have wide bolsters resulting in the side frames being closer to the outer edge of the car body than trucks designed for 2 rail wheels.  If you retain the 3 rail trucks and just replace the wheels with 2 rail ones  (I find .045 wheels to be a good compromise between looks and reliable operation) you've addressed the operational issue but not mitigated the appearance one. (admittedly I'm ignoring P48 gauge trucks).  One option to consider is selling the 3 rail trucks and installing 2 rail ones.  My go to replacement for Bettendorf freight trucks has been Intermountain trucks and wheel sets (they require minor assembly).  They look and operate well, and can be found for under $10/pair.  

The appearance issue is very subjective.  You might try re-wheeling one car with 3 rail design trucks and putting 2 rail trucks under a similar car.  Compare the appearance and see if the difference matters to you.  

Thanks for the great information. The cars are mostly Atlas and MTH freight cars