I built my cold air setup using a '74 B-body (Bonneville) air cleaner, adding a second snorkel. I used an angled plastic duct from a B-body on the passenger side, and a straight one from an X-body (Ventura) on the driver's side.
Both are plumbed into the cowl using metal tubing ducts that I fabricated, one has 3 tabs welded to the tube to attach over the hole that used to hold the wiper motor. The other one has a tube welded to 1/8" thick plate that covers the hole where the heater blower fan used to reside.
I didn't have to cut or drill anything on my car ('64 GTO) to plumb the air to the cowl, since I had removed both the heater and wipers from my car these two holes were available. The holes are both plenty big enough to flow all the air the engine needs.
I think I spent about $30 at the local Pick-Your-Part for all the factory components.
