It is a "1" but your link/links do not work for me.

http://chevy.oldcarmanualproject.com/chevyresto/5052.htm

1950 216 in a 3100

943391-1000 = 942391st engine out of that plant that year.

That engine sequence number is quite large. It most likely will have a late-in-the-year date/month.

Find and post the head date casting code and the block date casting code.

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.