I model Union Pacific circa 1952. I have some old Athearn "GP-9" chassis hanging around. I recall some attempts were made to produce aftermarket body shells over the years that would fit the older frame with the correct body width, etc.
Modelling Union Pacific 1952 in HO- Cedar City, UT branch and a tiny freelance iron mining connection to that
Huge V&O fan
Started back in 1977 or so
I wrote one article for MR - on a BASIC program for train maintenance forms January, 1986
Not sure what your question is Erik, but Front Range and CMR Products come to mind. ?
I think there might be a couple of Canadian products out there, too, can't think of their names.
Mike.
EDIT: Just thought of a Canadian Co., Kasslo Shops. I think their shell is made for a P2K chassis.
As a side note, I have a detailed Athearn GP9 shell I'm putting on a P2K GP18 chassis. Just need to do a little filing on the nose weight.
My You Tube
Erik...I recall some attempts were made to produce aftermarket body shells over the years that would fit the older frame with the correct body width, etc.
I'm not familiar with such body shells, but the Athearn chassis for the Blue Box geeps would need to have the raised areas within the long hood (alongside the walkways) removed to accommodate a shell with a narrower hood, and the method for mounting the trucks might require modification, too. Athearn's wide hoods were a concession to the motors they used, and I believe that their SD40 was the first with a prototypical-width hood. You'd likely have to replace the original motors, too, so it might make more sense to either pick up some pre-owned Atlas or Proto geeps, or simply use the original body shells on those chassis, perhaps with some detail upgrades and better paint.
Wayne
I think Front Range made bodies, though they are a little hard to find and the detail is no longer state of the art.
I would suggest looking at Proto 2000 Geeps. They have Athearn-like mechanisms, excellent detail with lots of little add-on bits, and can be bought for reasonable prices ($40-60) on Ebay or at shows. Depends on how eager you are to take on a project with those old Athearn frames. :)