So according to Wallace Racing in 70 there were two #16 heads, so is the difference there in the HP numbers which ones would be press in studs vs screw in studs? My other source I have looked at is http://ronspontiacpage.com/reference-pages/stockheadspecs.htm According to this he says that the year may reflect the casting date. It also includes many more years with #16 heads including RAIII which Wallace Racing doesn't list. I supposed the only way to really know is to look at the studs and measure valves. I have been assuming its some of the weaker heads but I had a little hope they may be better.