Still a newbie .. could use some help and advice..1971 Sierra 2500

[ItzhakRoberto]

So i've got a 1971 GMC Sierra 2500
I'm trying to figure out what size engine I have... this is my first American vehicle and I haven't ever really looked into it before so i've got no knowledge on this. I bought this truck off a coworker who had got it into an accident, and i already collected all the body parts but now i need some help with mechanical/engine parts. There are some things that got damaged, being the radiator, ac condenser, water pump, crank pulley, fan, fan clutch and that pulley, water pump......maybe the steering...
But what i need help is figuring out what engine size i have.
I don't want to buy parts for the wrong engine.
I don't have any pics right now ...hope someone can guide me in the right direction
Thank you