Jason-
The 4643k cars as far as I know were never made, but Lionel (as K-Line by Lionel) did make a set of 18" Milwaukee Road passenger cars in the Olympian/Hiawatha scheme. Interestingly Lionel did release a 21" version of the Milwaukee Road cars in the later 1960s paint scheme, again under the K-Line by Lionel brand name.
-John