Boy that's a close one as the Milw. E7's were built in 1946-1947 and that's exactly the same time the Milwaukee Road was upgrading the passenger car fleet.
Taken from Wikipedia...
"Two sets of passenger diesel locomotives appeared in 1941: a back to back pair of Alco/GE DL-107 locomotives, the #14, and a back to back pair of EMD E-6, the #15. The Twin Cities Hiawatha was partially equipped in May 1942 with coaches, two diners, and two ‘Tip Top Tap’ cars which ran with the 1939 Beaver Tails and parlors. Older series of cars were modified with skirting to run with the newer consists. During the following War years, the trains were loaded out to 15 car consists, and one of the 1942 cars painted in patriotic red, white & blue proclaiming “Buy War Bonds.” The train was so full, that people had to sit on suitcases, or stand in aisles.
In 1947–1948 the Milwaukee Road again re-equipped its major passenger routes with new lightweight cars. The new Morning Hiawatha and Afternoon Hiawatha were inaugurated with diesel-powered trains designed by Brooks Stevens. The new trains included the Skytop parlor observation cars. These four cars had a drawing room and swivelling parlor seats, and at the rear there was a lounge area with an expanse of windows. "