Help me decode my motor!

[1968_K20_4x4]

Looking for someone to help me figure out what motor is in my truck. The casting on the block on the drivers side towards the firewall is: 3956632. I read that this makes it a 307 from 1969. Is this right? Also, on the front pad on the passengers side there is stamped the code: VO428U5 (The last number is definately a 5 and not an S. I will post pics soon) I have not been able to find this code anywhere. If anyone can shed some light on what I have here that would be great!