Mark,
The Railsounds chassis will fit just right in the CSX waffle boxcar and the waffle boxcar has the 4 corner posts in the same positions as a Railsounds car. I measure the "footprint" as 1 20/32 wide by 7 5/8 long in both cars.
I've already put my Railsounds car in a different shell. This UPS boxcar is from 2007 so it has the four posts in the corner. My camera work makes it difficult to see the corners of the CSX boxcar but the "upper" two screws are just visible. The CSX is actually a bit longer because the ends of its shell wrap around the chassis rather than sit "above" the chassis. You can see that in the 3rd picture.
Craig
