I used TTI headers 400SR218 for my 400 install. Didn't have to dimple dent cuss or well maybe some cursing.
The engine plate did help because I moved the engine up a half inch to clear the pitman arm, unsure how the Schumacher mounts would go.
I also have electric power steering so there is that.
Spark plugs will be a chore unless you have 3 elbows or willing to cut an access panel on the inner fender. #6 is my evil cylinder.