E 21 5 is one casting number (block)
April 21st 1955

Engine Serial Number: 0327699

Here are 1955-1st Engine Serial Number codes:
http://www.1954advance-design.com/chev-specs/1955-1st-Chevrolet-t-ser.pdf

Here are 1955-2nd truck Engine Serial Number codes:
http://www.1954advance-design.com/chev-specs/1955-2nd-Chevrolet-t-ser.pdf

Here are 1955 car Engine Serial Number codes:
http://www.1954advance-design.com/chev-specs/1955-c-ser.pdf

Your code does match either format.
Maybe someone will correct me, and/or explain/decode.
It might be a replacement engine?

Tim
1954Advance-Design.com
1954 3106 Carryall Suburban
1954 3104 5-window pickup w/Hydra-Matic
The 216 and early 235 engines are not "splash oilers" -- this is a splash oiler.