Andy : The exact answer to your question on lettering is somewhat complicated (like all early Lionel stuff). The "Brown Series" was offered in 46-47-48-49 with the differences being the engines that they came with and the color & number in the lettering.
In 46 they came in sets 2100/2100W with a 224 loco and either a 2466 T or 2466WX (W means Whistle)
In 47 they came in sets 2120S/2120WX with a 675 loco and either a 2466T or 2466WX tender
All lettering was Silver in 1946 and White in 1947 . Note color scheme was brown sides and roof, Grey Door and window inserts, and the brown cars always came with lights
They came back in 48 and 49 with Brown color again BUT the numbers changed to 6442 for the pullman and 6443 for the observation. Color scheme (brown/grey) was the same and they had lights. Lettering was white.
In 1948 they came in set 2136 WS with a 675 loco and 2466WX tender in 1949 they came in the same set, 2136WS, but the 675 came with a 6466WX tender.
Clearly if your cars were in the 2400 series they were produced for the 46-47 outfits. If they were in the 6400 series they were produced for the 48-49 outfits. All these cars were brown.
The most scarce are the Brown cars with the silver lettering. these were only made in one year 1946. The others are more rare than the common Green series however there is also a two tone Blue series which carries yet a 3rd set of numbers and is even more rare - postwar however it is a pre-war carryover and is more common with the pre-war trucks. MOST IMPORTANT - as far as I can research 2442/2443/6442/6443 cars were always BROWN and 2440/2441/6440/6441 cars were always GREEN. the lettering changed from silver to white in 47 and never went back. 49 was the last year of the tinplate cars.
I know you were thinking of painting them GREEN and the GREEN series covered all these years but the car numbers, set numbers, and loco's in the sets were different. I can give you those if you want. There really is no question however that the brown cars, especially those with silver lettering are far more scarce.
Best Wishes and Good Hunting. Hope to see pictures of your re-hab'd cars when you are done
Don
