This would be one of those times, that if you have to ask, you probably don't have it.
The stage II program was a heavy duty (ie. racing) engine program that Buick had in the 80's. Most of the motors were used for drag racing, and Busch Grand National Nascar racing.
Unless you've got a race motor, you probably don't have it.
One way to tell though, is to look at the back of the block near the freeze plugs. It will have the Buick Power 6 logo cast into the block.