I made a jig from some steel flat and some drill bushings. It was a lot cheaper than buying one.
I did two pair of 062 heads. The intake faces were, oh, maybe a bit over 1/8" thick. I used 5/16" fine thread bolts to get more than two threads. Both pair of heads worked, but I always felt it was a very iffy deal. A hair too much on the wrench, and you'd be trying to figure out how to braze in a Keen-Sert or something.
Maybe not all of the heads are that thin, but I'm not happy at all with the thread engagement of the ones I did. I suggest you drill some small pilot holes first, just to see how thick your heads are, before doing this.
If I was racing in one of the stock intake/stock head classes, I'd look for one of the GM four barrel marine intakes before I'd drill another pair of Vortecs.