Choosing a model car fleet-SP 50-ft. box cars

Concluding my posts about the SP box car part of my model fleet, in this post I discuss the 50-foot cars. These are single-door box cars. In the period I model, the AAR defined double-door cars, whether or not 50 feet long, as automobile cars. Those are accordingly a separate subject in my planning.
     Southern Pacific had just two classes of 50-ft. single-door box cars, classes B-50-22 and B-50-30, by 1953. The B-50-22 cars were built in October and November, 1941, to essentially the AAR 1937 car design, stretched to 50 feet. The AAR would adopt a “standard” design for this type of car in February 1942, but the SP box car was not of the AAR design. The design SP used had six panels on each side of the door, panels which looked much like those on the 1937-design 40-foot cars. The new AAR design, however, had eight narrower side sheets on each side of the door. Many railroads in the late 1930s also used the 6+6 panel design, so SP was far from alone. But there were just 500 of these cars built by SP (numbers 81490-81989), so I only need a single one in my fleet. The SP attempted to buy 500 more cars at the beginning of World War II but the order was never fulfilled.
     This class is fairly simple to model. The Proto2000 model (now Walthers) is very close to exact for the SP cars, having the 6+6 panel design, a straight-panel roof, and W-corner-post ends. Here’s the one I already have (there’s a kit for another one, gathering dust in my stash).

What about the old Athearn version? Is it usable? It’s certainly a stand-in with about the right look. But correct? Nope. It’s got sharp-corner Dreadnaught ends, not the correct W-corner-post ends; and it has the curious Athearn 50-foot car roof, which Athearn’s double-door automobile car also has--a roof with 12 panels instead of the correct 13. (Hard to know how this happened.) And it has an odd 6-and-a-half panel side design.
     The second class of SP 50-foot single-door cars was B-50-30, built in late 1952 and early 1953, just under the wire for my modeling year, 1953. This time there were 1000 cars built (SP 109100-110099), so again, at my ratio of approximately one model car per each 1000 cars in SP’s fleet, I need one model. But now the problem is that SP continued to build 6+6 panel cars, while nearly all other railroads were building 8+8 panel designs. There is a fine model available for that 8+8 car, the Branchline kit with correct Improved Dreadnaught end, diagonal panel roof, and 8-foot Youngstown door. You can do two things here: either use the Branchline car as it is, and never notice the number of side panels whenever you spot the model on the layout (for me, kind of like not thinking about the elephant in the room), or you can fix it.
     I plan to fix it. Here’s a photo of the Branchline car (from their web site), and my intention is to slice off all the rivets, sand off the panel seams, scribe new seams to make a 6+6 panel car, and replace the rivets with Archer rivets.  (And one more detail: I will re-letter it too.) I’m willing to do all this mostly because I only need one car. But it also looks (so far) like an interesting and fun project.

So far I’ve only gotten as far as slicing off rivets. More later as I make progress.
     This model fleet discussion, like several others I’ve posted, has served as much to tell me what cars I don’t need, as to tell me what I do need. I find such discoveries both illuminating and very useful.
Tony Thompson