Steering Shafts hitting headers is a header design issue. Not a motor mount issue.
With LSx motors most run into that issue trying to run 2" Primaries. SOMETIMES 1-3/4" but rare. Most people will just dimple the header in, or run an additional joint. I know some that had to do a custom setup to kick out the shaft and bring it in.
Old LT1 Shafts are the worst due to a big huge lump in the middle, that always interfered with headers. (see LT1 Rag Joint)