The number on the body tag is technically the model number. It does not contain the last digit of the model year as the VIN does. Models were coded as follows:
1=Chevrolet
23=6 cylinder engine
24=8 cylinder engine
37=hardtop
67=convertible
For reasons not known Fisher Body did not fully adhere to this. Fisher stamped and referenced the body tag during body fab. They only used 12437 and 12467.
When the VIN tag was created by Chevrolet, the model number was correctly specified:
12337 = 6 cylinder hardtop
12437 = 8 cylinder hardtop
12367 = 6 cylinder convertible
12467 = 8 cylinder convertible