I will probally get hammered on this one as this is a hot topic as we speak. You can do a search on the board about GN1'S. Some guys love them, some hate them. From what i have read there were some issues with the early castings, however i myself have a set of GN1R'S for my S2 engine, you can see that the casting is a little differnet than early GN1'S, Alot more meat around the headbolt area. I have not heard of as many complaints with the newer castings. If i was in the market today for heads, i would probally wait to see TA'S heads, it is based off the MA casting with major improvments for cooling and durabilty. Just my 2 cents...
Enclosed is a pic of my heads go to S2 folder.
http://photos.yahoo.com/bc/travis951...N+PICS&.view=t