wat engine do i have?

[blowthedoorsoff]

i have an 81 gmc sierra 3/4 ton that i just pulled out of some bushes. Pulled it into the shop dumped some gas in the 4-barrel carb and it fired right up.. . only problem is, not sure wat size the motor is. Its a v8, original motor was a 400, but not sure how i can tell whether its a 305/350/400 that is in it. I know there is a number on a hard to reach place on the block, but i was wondering if there is any other distinguishing features that anyone knows about that might help me determine what it is. Thanks

[2000CAYukon]

You need the casting number off the block. See http://www.mortec.com/castnum.htm

There are links on that page that tell you where to look for the numbers.

//2000CAYukon