The other item is that the 4200 is current produciton - easy to get parts for. And most likely it will outlive the rest of the vehicle. I read somewhere GM ran a number of these engines wide open for like 100,000 miles and they were as good as new, so they reduced the number to like 3-4 and ran them until they got kicked out of the dyno cell at 300,000 miles. Yikes!
http://media.gm.com/division/powertrain/news/4200_Overview.pdf
