273 casting number question
A quick look under the left front head where it meets the block will reveal a stamping pad and the year confirmation for the 66 273 block! You are looking for a capital "B"stamped there, indicating a 66 year block! Casting dates are a general parameter, but the B stamp indicates that it is built for a 66 car!
Pic of the area with a B stamp, from a 66 motor from a Cuda! Stamp says B273 4-12, indicating a 1966 273 with an assembly date of April 12th!
Incidentally, the motor I pictured has a casting date of 3-3-66...March 3rd 1966!! Interested? PM me!! Geof