Identify the origin of an LS1

[Formula400]

Hi!

After having searched the web for ages I'd thought to ask here if anybody know how to identify an LS1 and by that I mean from which car was it taken out from and what kind of power the engine was supposed to have.

Here is some information.

At the rear of the block on the driver side is the following number #12559378 (Which should make it a 99+ block, I was told it was taken from a 2001 Firebird with the WS6 package)

There is another number on the driver side at the face where the transmission faces up. #H242 074 and #212138215

Heads number is #241 (There is another number on the driver side head but don't have a picture of it)

And finally a assembly code of some sort on 2 places on the engine. (On the rear driver side head and on the driver side at the front on the block) #10YHB K010460431

Any help appreciated.

//Sven