Engine Identification

[wydomkr]

I just got a 69 C-10, 6 cylinder, 4 speed, from a guy because it wasn't running. The gas tank was so full of crap, the sending unit tube was plugged solid. Replaced the fuel tank and sender and it fired right up. Now I'm fixing some other things on it. He told me it had a newer engine in it which I believe is true because it has electronic ignition. My question is, how do I tell why size this engine is, I've never had much to do with 6 cylinder engines. The exhaust manifold is broke at the flange where the exhaust pipe bolts up and I need to get a new one. Or would I be just lucky enough that all straight sixes used the same exhaust manifold?

Keith