CAUTION, be very careful! Northstar engines have a tendency to develop oil leaks with age that cost an arm and a leg to repair! I'm talking several thousands of dollars! My uncle owned an Oldsmobile Aurora that was completely pristine and didn't have that high of miles on it. It had a Northstar engine, and one day it started to develop a bad oil leak. My uncle had to sell the beautiful car for dirt cheap because of this.
Also, I almost bought a Cadillac STS that had a Northstar motor. It was in perfect shape and I really wanted to buy it, but my dad recommended that I take it in for a pre-purchase inspection first. The repair shop found out that the car had a serious oil leak that the dealer was trying to hide. They said "don't walk away from this car, run from it!"
That might not be the case with this car, but that is a lot of miles non the less. I'd stay away from any high mileage Northstar motor!