21FP-K 9710

21 = Janesville plant
FP = 1948 3100
K = 11th month = Nov

http://www.1954advance-design.com/chev-specs/1948-Chevrolet-t-ser.jpg
http://chevy.oldcarmanualproject.com/chevyresto/48index.htm

All Suburbans prior to sometime in 1950 had the End-Gate/Tail-Gate/Lift-Gate (clam shell doors).