According to most sources, the 3970010 casting was used for '68 327, and '69-'79 or '80 350 engines, and possibly one year for a 302, but not the 305, which has a different bore.
Two numbers don't add up here. Assuming a 350, which didn't come out until '69, the block date code would be from '78, but the second digit of the VIN code (6) suggests '76. Could the 8 in the block date code really be a 6?
The engine build date of May 13 seems like a close enough fit with the block casting date of April 22.
Sources show the CMJ suffix as a '74 police 350 4-bolt main (or an '80 Camaro/full size 305, which doesn't apply here). '74 doesn't match the VIN year (or casting year), but I suppose it's possible that the suffix carried over to '76 without the sources showing it.
The only definitive thing the numbers tell us in this case is that this is a 350 block. Internal details would have to be determined by inspection.
