Onemangang,
It didn't take very long at all. I used a standard drill bit and hand drill, don't recall what size the bit was, it was the size that edelbrock recomended in there write up, will have to see if I can find it. I drilled unitil I hit the water jacket, those victor jr. heads were pretty thick in the area I drilled.
I would still get with your head manufracturer to be on the safe side before you drill into the head, to see what they recommend to do.