Intermountain part 60050 is for current Atlas trucks. FVM also has axle lengths which fit these trucks. Check your favorite retailer. I've found the distribution channels for IMR and FVM wheels can dry up pretty quickly, so get them while you can.
My track isn't good enough to handle standard width treads, at least not how I like to run. So when considering a change, you might want to first test before investing in a large number of wheels.
Bill Kepner