Get the number off the driver side rear of the block behind the head by the bellhousing.
The problem is, I've had blocks laying around before and I've seen where the numbers normally are... this engine has no numbers anywhere. Seriously. I'll post the pictures I have of the engine from when I first got it.... In the first picture under the wire loom to the left is where the number is supposed to be. I'll try spraying degreaser back there and looking again!