28 degs. on a new mill won't hurt it--yes, the exhaust temp will be a little hotter but take it easy starting out--the dyno guy has done this before, take his advice, he knows what your motor was when it left his shop--check back with him if you make any boost changes, or carb (hat)changes-- hard to say how much total u can run without knowing what the blower is doing--go with the dyno man---be safe and watch out for the other guy