John,

Welcome to Stovebolt.com

839770 was used from 1942-1947 on 216 engines.

There was an E preface in the Engine Serial Number in 1940
http://chevy.oldcarmanualproject.com/chevyresto/4010.htm

There was an AE preface in 1941
http://chevy.oldcarmanualproject.com/chevyresto/4110.htm

AECA preface does not match a 1942 code, but it is close (2AE).
http://chevy.oldcarmanualproject.com/chevyresto/4206.htm

It might be a WWII era code. The website I used for those codes has vanished.