[Arran]

I think what others have said probably explains it, they lined up a deal on a rail car full of type 41s and chose those rather then a pair of 7A5s or a pair of 6K6s. Interesting that your set uses a 5Y4 with a pair of 41s, many early 40s Philcos used type 84s, 80s, and 7A4s. I saw a Canadian market Philco Bakelite model that was AC, not AC/DC, that used 2.5 volt tubes like a 58s and a 2A5, and it was from the early 40's, obviously they designed the set around the parts.
Best Regards
Arran