<<Along with the 10 boxcar recommendations for Jason, I am looking for an accurate HO model (prefer RTR but will do kit if required) of a steel GN 40' boxcar that would fit the fall 1956 era for my B&O Shenandoah SD layout.>>
My comments apply to both the kit and RTR versions of the following models. You’ve received several answers; here are some caveats about those options. Their acceptability depends on your definition of accurate:
1) Intermountain GN Plywood sheathed cars – pretty darn good, but some have commented that the ends of the frames on the side of the car below the plywood sheathing are not as deep as they should be.
2) Intermountain 12 panel steel cars – If you are finicky, these are truly accurate for zero to one and a half series of cars.
a. If you have the version of the car/kit that does not have the narrow top rib across the top of the end, these kits/RTR are correct for the 2525-2549 series with the 7 panel Superior doors, and those cars in the 10900 – 11374 series with the same Superior 7 panel doors.
b. If the kit has the 4/3/1 ends, remove the top “/1” rib, and use either the supplied Superior 7 panel or acquire an aftermarket 4-6-6 Door from Southwest Scale Models (also available from time to time through Andy Carlson).
3) The Intermountain car can be used for the following GN series, but the following caveats apply depending on one’s level of finickiness ™:
a. All – straighten out the bottom of the top rolling pin on the side (match the bottom of the rolling pin to the bottom of the “rolling pin handles”;
i. Series 11375 – 11874: Use a Superior 5 panel or a Youngstown 4-6-6 (Southwest) depending on the photo you are using (Still need to correct that top rolling pin).
ii. Series 18000 – 18499: Use the Intermountain car as is, using the supplied 7 panel Superior doors (Still need to correct that top rolling pin).
iii. Series 18500 – 19499: In addition to a. (above), use a Southwest 4-6-6 door.
iv. Series 19500 – 20499: same as series 18500 – 19499, though my notes suggest the grab irons might be double drop grabs instead of single drop grabs.
4) The C&BT 12 panel car can be used for the following series. My comments are limited to the shells without cast on details, someone else will have to speak to the appropriateness of the C&BT cars with cast on details:
a. Series 20500 – 21499 – As is, plus aftermarket details – Detail Associates FK501, and others
b. Series 21450 – 21939 – As is, – Detail Associates FK501 plus aftermarket details - Detail Associates FK501, and others.
5) The C&BT 12 panel car with 8’ door can be used to model GN series 21940 – 21949 , Detail Associates FK501 – plus others.
All of the above can be improved beyond what I’ve mentioned by using additional aftermarket parts including Apex running boards, etc. I’m not enough of truck expert to specify those (I’m working on that!).
Andy Carlson can be a great resource for additional detail options for these and other cars.
Other options for GN boxcars in (relatively easy) kit format include the Accurail Double Sheathed cars.
Bottom line, the suitability of any of the above cars is in the eyes of the modeler.