[C10 - C90 Bill]

I agree on the 5500. Also by a couple of details in the pictures, the truck is either a '66 or '67. The Title very well could be correct listing it as a '67.

My best guess is that you have either a 305 or a 351 V-6. There are numbers on the block at the front of the engine that would tell you for sure, as Okiefromwatonga has provided by the link he posted.

Bill