All of the 3946074 heads had provisions for two additional studs (per head) that were used in conjunction with the additional bosses on the ZL-1 aluminum block.
In the event that the heads were used in a non ZL-1 application (a second design 1969 L-88 or 1971 LS-6 for example), the studs were still present in the heads, as something was needed to seal the holes in the intake ports in the heads. I was fortunate to look at a rough, but relatively untouched 1971 LS-6 Corvette this past weekend and this is how it was done. It looks a bit odd to see the ends of the studs just hanging down like that...
In any case, the holes in the intake runners are going to have to be sealed in some manner. There is also a machine shop somewhere in the Cleveland, OH area that can weld the bosses onto a cast iron block for those so inclined.
Hope this helps.