Bill, you are 100% correct....
in 1941 the 1 ton is a downgraded 1 1/2 ton (wheelbase 134 1/2").

Basic Models - 1 ton RPO
http://chevy.oldcarmanualproject.com/chevyresto/4104.htm

RPO becomes 1 ton
http://chevy.oldcarmanualproject.com/chevyresto/4107.htm

Rear Axle Serial info
http://chevy.oldcarmanualproject.com/chevyresto/4110.htm

4.55 or 5.43
http://chevy.oldcarmanualproject.com/chevyresto/4114.htm

Also, in the 1929-1950 MPC,
Group 5.505
part# 3682125 is listed, but with no casting #,
as 1946-50 All Comm (exc. 1/2 ton)


-Tom

1950 Chevy 3100 w/ 1956 235