Like gary says, the way to tell what engine you have is to find the casting number. Its behind the driver's side head, cast into the block next to the bellhousing.
Go to Mortec.com and they have most popular casting numbers for SBC blocks. I ID'd an engine for a friend's car. Block code was 3914638, which was a '68 327. Those numbers on the front of the engine don't tell the whole story, as they were reused on different engines over the years. That 327 was thought to be a 283, because the "DH" code on the front could mean either a '58 Corvette 283 or a '68 Truck 327. The block casting number positively IDd it as a 327.
good luck
chip
OH, BTW, the 283 was made from '57 to '67. The 327 was made from '62 to '69 or so. :p
