As you get into this, you may find items such as the following useful:
a) a nice MR article on freight car trucks you can download
b) a couple of listings on the Reboxx site that show info on stock axle length, etc so you can help choose a compatible length with your replacement
http://www.reboxx.com/wheelsets.htm
Many folks advise to always use a MicroMart “truck tuner” or similar tool to ream the cone within plastic truck frames to remove burrs, etc to ensure a good axle nesting point. I also found it helpful to buy a moderate price (about $25) digital caliper to ascertain stock axle length when I was substituting. For freight cars I settled on 33" Intermountain primarily, Proto 2000 backup. Some folks like other brands (e.g., Kadee, Reboxx) alot also. The P2K I can get in either smooth back or ribbed back 33" wheels, the latter for older freight cars. Suggest you can do a roll test on a slope with rollout and easily see big differences as you work on this.
There are a number of older threads on metal wheelsets but I have limited luck with the search feature. An example follows.