I don't know how helpful this will be, but here goes-
The closest WoT baggage car is the 70' car when equipped with a clerestory roof. These are very, very close to the cars 1400 and 1401.
The problem you (and I, and anyone who wants to model the "standard" L&N baggage cars) have is that the vast majority of the L&N baggage car fleet were 70' long, and had symmetrical doors that were 5'6 or 6' (approximately), and no such car exists in N scale- all the 70' cars have one large door and one small door. Cars up to 1472 were clerestory, 1473-1490 were arched roof.
The photo in the OP is lettering circa 1960 something. For 1950s, you would see the conventional "Railway Express Agency" lettering. Decals are available from "Great Decals" which has a set that will letter any L&N head end car post WWII. Also, in 1950, some cars may have still been painted dark green with block lettering (this was still true in the late 40s).
Doors are a good question, and the best answer is, probably, I don't know for sure. The earliest dated photo with modernized doors I can find in my books is 1952 (one of the combines remodeled into a dorm)- so they were in use on some cars by that date. Another photo is dated 1962, and shows 2 baggage cars- one with conventional multi-window doors, and another with the single center window. But based on photos generally, most baggage cars had single window doors by 1962. My speculation is that sometime after WWII, L&N started replacing doors as needed, with the new style steel doors. I have seen no photo of a car with old style doors with the "REA Express" lettering, and no car with modernized doors with the early "block lettering" style. The Palmer script lettering with "Railway Express Agency" on a blue car can be either in the photos I've seen.
As is frequently the case, best option would be to find a photo of a particular car in a particular year.
Color is a matter of opinion.
The colors I've been using are Modelflex L&N gray for the roof, and Model Master Blue Angel Blue (which is, of course, since I am using it, no longer available). In your photo, at least on my screen, the color is "blacker" than it usually appears. I've seen cars done with both B&O blue and C&O "enchantment" blue, which also look good. Do a search for the photos of L&N models posted by altohorn25. I also read one article that suggested ATSF freight loco blue.
Bob Chapman had articles on L&N Baggage cars in the June 1993 "Dixie Line" (L&N historical society magazine- they had back issues last time I looked) and Feb 1995 Mainline Modeler.
Another note- the L&N also had a small fleet of horse cars that spent much of their time in baggage and express service (when not moving horses). The MTL car is very close in terms of door size and placement, except that, at least according to drawings and photos, the L&N cars did not have end loading doors on either end. But the car looks pretty good in L&N colors.
