And for comparasin, here's some pics of mine, original 318 car with a 440. The 440's a little taller and a little wider than a 383 or 400 so the fit is a little different.
Here's the passenger side. The bulge of the passenger side inner fender actually protrudes OVER the frame rail there, just killing space in that area. You can see where the tube touched my fender and blackened the paint a bit before I dinged the fender there. I just pulled the motor today and I plan to trim that area back so the inner fender is flush with the frame rail and weld in a piece of sheet metal so this issue isn't so bad. But other than having to ding the one tube/fender area(the back one of the middle two cylinders, the one beside it had a little room so was fine), the passenger side summit header fit perfect.