Depends on your intended power level.
Over the years Champion has been forced by the hard core Buick racers that push-push-push the envelope.... to redesign the castings to be stronger to take the higher HP levels. I can't tell you what each "generation" of casting is good for..... there is no number written in stone somewhere. What I can tell you is we cracked several of the early ones..... but we were in the mid 9 sec to low 10 sec power level. The later castings are beefier where they need to be to hold the power. I believe the newest casting to be good to 1500+ HP I'm told.
IMHO.... If your goals are in the 9's...... I'd stick with at least a casting where the GN1 is engraved in the end of the head. IMHO it will potentially save you frustration down the road.
The bottom line is... the original GN1 aluminum heads were never designed to go 9's..... the later ones are. The newer the gen head you have the better.... from a holding up standpoint anyway.
