289 head specs

Hey, do any of you guys know what the differences are in the earlier 289 heads, vs. a set of 68 289 heads? Does one set have larger chambers than the other? Can one set recieve larger valves than the other? Thanks for any info. in advance!

if you want a set of early heads with larger valves the early 351w heads had bigger valves, but the head wasn't like that for more than a couple years and was changed to match the valves on the 302 head. As for chamber size I'm not sure, but you can use thick head gaskets to make the chamber a little bigger.