That brings up a question: it is my opinion that the 1950s Lionel Budd extrusion was close to scale in cross-section. The baggage car may have been exact. Why wouldn't they have used that cross section for a 21" car?
Clark Benson sold 21" Lionel extrusions back in the 1970s. They were perfect except for that lower letterboard, which has no prototype.
No - the K-Line dome is not accurate for either Pullman or Budd. For one thing, it is too small.