Free 400 for me... worth it?

[toddtheodd]

I've got a friend at work that wants me to pull a motor for him. The motor is basically a short block with heads.
He said that it was a pontiac 400.
He also said that if I pull the motor for him, I can have it.
Now what I'm needing to know, is how I can tell if it is indeed a pontiac 400, or something else.
I'm guessing that a pontiac 400 would not be compatible with my transmission. So would it even be worth it to take the motor, or would I just be taking something that I can't use?
If nothing else. I figured I could use the crank to make a 383, unless of course it's not really a 400. (The person he bought it from didn't really know anything about trucks or motors, he just comes across deals a lot)
What would you do?
How can I tell what I have?
Todd