c body exhaust manifolds on a 400 in our duster

I used the Schumacher /6 to b block motor mounts. I don't know if I have any problems nitro, just wondered if they are all that right of a fit on the passenger side like these are. If I didn't grind the rib off the passenger side wouldn't have fit. But going by kimmers experience with them, something is off. They are off a 1970 sport fury, which if I remember correctly is what Schumacher recommended as far as in the year span.