For some reason I got the 40 ft DD boxcar bug after Martin left us and had a terrible time finding those cars at what I considered a reasonable price.  But I started using the CB&T, McKean and Front Range kits with new doors and ends and other appliances and they look great in my opinion (yes of course I'm biased).  Here is the B&O M-59 from a  Front Range kit and Chad Boas made the ends, doors and side sill reinforcements.  Also the SAL AF-4 using a McKean kit with Chad Boas ends and doors and side sill reinforcements.  Chad has been very helpful with freight car parts but so has Speedwitch and several others.  So go for it.