30 degrees are a modification, based on the idea that you get more curtain are quicker at the cost of somewhat weaker centering and seating. I don't want to guess angles from an online picture, but you should be able to tell dif between 30 and 45 with a very crude inspection. Go to the shop manual or an experienced builder for a width spec and follow it, and on the one degree difference bit...ask the shop what they did, as that is not a universal practice.
The Jalopy Journal
