You might be able to loosen the inner fender brace and slide it in between the inner fender and the brace or just bolt it to the outside of the brace but for it to be correct it goes between the brace and the inner fender.
As I think back when I pulled out the original 350 some 38 yrs ago in the early 80s that 5th seal was in place on the drivers side and separate from the two smaller splash shields that bolt in between the inner fender and the brace. Of coarse being the stupid 20s something kid I was I pulled it off because it was in the way of the bellcrank lol. And the piece that it mounts to is long gone .