I thought I knew what you were talking about, but when you mentioned gear boxes, that threw me. Maybe you meant draft gear boxes, which means Talgo trucks. Talgo trucks are almost always a bad idea on most freight cars, although there are exceptions. You said the car already has body mounted Kadees. That means just about any RP25 AAR truck would be fine, the higher quality the better. Some folks prefer the narrower wheel treads for appearance, but true fine scale treads require special trackwork, so you probably shouldn't go for P87 standards.
Ribbed backs indicate the wheels represent iron wheels, which had the ribs to prevent overheating. Most of these were phased out of prototype use around the 1950's and replaced with non-ribbed steel. On a model, there is no operational difference, and it's hard to see from trackside in most cases anyway. There are much more important things to be concerned about.
Tom
I have built many of those old Athearn metal kits (the floors are wood) which Menzies re-released around 1980 for a brief while.
The trucks that came with them were old Athearn metal trucks, which often I would just replace with the comparable Athearn plastic trucks, so-called Bettendorf (which is actually a particular trade name and not a "type" of truck). The ribbed back wheels were phased out in the 1950s, probably after Athearn stopped making those metal kits, so what you found on Ebay should be ok for at least some cars in the old Athearn line, although smooth back wheels would be OK too. The bolster should mate acceptably with the bolster on the car itself. But likely so would many brands of freight car truck, including Walthers and Athearn itself.
One caveat. Athearn made a metal kit for the Timken roller bearing boxcar that was sent around as a sort of advertisement by Timken. For that car of course you would want a model Timken roller bearing truck.
One other caveat. The frame is metal on those kits. If the trucks are metal then you need to use plastic wheels or make sure the insulation of the metal wheels is all on the same side of the car to prevent an accidental (and maddeningly hard to trace) short circuit. Back when many cars had metal trucks, metal frames, and metal couplers, a short circuit could travel from car to car to locomotive, and you'd go nuts trying to resolve it.
Dave Nelson
I need so sound advise, I resently purchased a box car, an Irvin R Athern metal madel, at a train expo - the couplers are attached to the box car body (replcaed with Kadee #5 ) I want to replace the trucks but I don't know which to choose. I went on e-bay and found Bettendorf metal trucks w/33 ribbed back wheels code 100 with out gear boxes which would you use? BTW all attached by machine screws :-) Thanks for you help
Angelo
Freelancing MCRR/NYC Northern Division - Angelo