I would ask a few questions first, the number you provided sounds more like a VIN number stamped on the engine than a producton number I have 2 Northstar engines out in the garage one is from a 2001, one from a 1996 both have a 6 where your number showed a 6. The final 8 numbers are the year and build sequence.
I have access to GM's web site to check out VIN'S so I typed in that number and it shows that vin was built as a 1996 DeVille with the low horsepower "Y" engine (275-285? I can't remember which).
It was sold 5/15/96 in Smyrna, GA It was last in a dealership for the fuel rail champaign on 12/19/05 at 73,023 miles.
So check closely before buying, there is nothing wrong with a good used engine, but I know I would not want to spend $2-3K thinking I was getting a new engine and receive a used engine worth $1000 or less.