340 block- Casting #s, Vin#s, And Assy #s

CFD244 said
This number on the block, under the driver's head, from what I understand...........

The letter in front of the "W" denotes the build date.
D = 1968
E = 1969
F = 1970
G =1971

Etc.

Maybe the M is for Marine, or replacement? Just spit balling.

I’ve corrected the original post with a F instead of M, I have no idea how I keyed M instead of F, I guess it was a Senior Moment.
FW340P32250498