The 452 intake port approaches the seat at a lower angle as compared to a 906 casting. I usually use back cut angles between 27 and 30 degrees on a 452 intake valve. Unless you have a way to see what your port likes, I would stick with a 30 degree back cut. If the 30 degree back cut gets to wide, sometimes I will narrow it with a second back cut angle. I do not use any back cuts on the exhaust valves.

Jim