wheel openings

About a year ago I seen a 66 dart with the wheel openings cut like the 67 hemi dart are and they look good . That's why they would look even better on my 64 dart.The tires now are 29/12/15 I want to go 2 to 3 inch's wider 1/1/2 iner 1/12 outer on a 15/12 rim