Making progress.

I used this website for info:

http://home.znet.com/c1937/Cast.htm

Cast number 3837004 it says is 55-57 Chev T56X engine with displacement 235-261

Date code CON4 I 21 6 = Sept 21,1956 cast date

and stamped serial number F926A

Is there a way to confirm 235 or 261?