Bob
Thanks for chiming in. As I said, I know the Hill Lines well but PRR prototype rolling stock is not my specialty. Any additional info you can add would be most welcome.
I agree that the X29s from Atlas are well researched and nicely done. That isn't always the case regardless of manufacturer. I have a few beautifully decorated box cars with prototypical paint schemes and authentic car numbers. They are nicely detailed with well executed grab irons, ladders and running boards. They aren't X29s but they are from Atlas. They don't even match the dimensions of a brick scaled from the prototype. I'm not sure how one would categorize them as models.
The prr.railfan.net site that I linked above says of the X29B that they were rebuilt between 1940 and 1950 and had "Corrigated Roof & ends". The photos of X29Bs on that site show improved dreadnought ends and diagonal panel roofs which would have come on the market in the later years of the rebuild program. Early X29Bs could not have had those roofs and ends since they had not been manufactured yet. Were Viking roofs used on some early X29Bs? If so, the MTH or the less common version of the Atlas ARR box car would be a good candidate for an X29B stand in. For the later X29E the Atlas Trainman box car would seem to be the closest starting point.
The MTH car is lettered as an X29.
I can't see the class lettering in Pro Hobbies photo. Do you have a better photo or one of these models? Do you have a reference that would show if PRR 6229 was applied to an X29 or any of the X29 sub classes? If PRR 6229 is not an X29 car number any idea where it might have come from? As a PRR fan do you have any additional on line references to recommend to those interested in accurate car types and road numbers?
Thanks for all the info. 
