help with 1968 pickup engine size

[thethirdbrother]

I just bought a 1968 GMC pickup and am trying to determine what size engine is in it. I do know that it is the original straight 6, but the guy I bought it from didn't know anymore than that. He was selling it for a friend, and so couldn't answer this question for me. This is my first vintage US vehicle (all VWs before this). What was standard for this truck, or is there anything about the truck that I could look at in order to determine the engine size? Any answers, suggestions, or general help would be greatly appreciated!
Thanks in advance for your time and responses!

[Mr_Mac]

Probably you have a 235CID six shooter. You can check your VIN on this site (http://www.americanclassic.com/paint.htm) to verify what your truck was equiped with from the factory.

By the way...where's the pictures?:(

Mac