I'm the Wiz, and nobody beats me!
Agreed on their desire to spend labor dollars and focus attention on the parts of the bike that the customer cared the most about or that were the most visible to them. But something still doesn’t add up with the difference in stampings between the 1 piece crank bikes vs the 3 piece crank bikes. Schwinn is investing in automation to reduce labor hours and speed production. The BB are starting to get electroforged and machine stamped for the 1 piece crank bikes around this time. But for some reason they are still sending the 3 piece crank BB shells down a line with guys using hand stamps to overlay an I and an O stamp to make a composite D. That doesn’t jive with the automated, labor reducing mind set we see them taking. There’s got to be something else going on. Something we don’t know about or understand yet.
There has to be a good explanation and reason for the hand stamping but it's probably buried somewhere! The one piece crank shells had machine stamped serials starting in 1937! And honestly, I don't remember seeing machine stamped BB shells for the three piece crank on the post war pieces until the late 40's. Looks like the three piece shells were machine stamped in 1949. @Oilit 's 49 New World.
And another note. There are no U serials listed on the 1949 SN list or for the 48 thru 51 numbers.