I have a 57 Chevy Bel Air frame I want to drill and tap in a few places. I’ve seen people do this for smaller screws that go in fuel rail brackets but I’m not sure the frame is thick enough for slightly larger bolts...I want to tap for bolts to hold trans cooler. Frame is boxed so I can’t get a nut inside and it’s powder coated so I don’t want to weld at this point. Anyone drilled and tapped frame with bigger bolts? Any can’t find any online guidance on minimum metal thickness for bolt size. Thanks.