OzyDuster74 full rebuild and hemi conversion!!
There are some threads here on locating the holes for cutting. I think there are also templates you can buy.
For the dual snorkel scoop, there are two holes near the rear of the hood.
For my dual scoops, the hole size called for 4-1/8" hole but that was a touch too big.The seals still fit and don't fall out but there is play in them. I would use a little smaller saw next time. I'd measure whatever gaskets you have and size accordingly.
DMT sells gaskets