The Us60 was designed for OS 61 FX with 11" prop, I fly it with OS 75 AX and I need to stop the vertical climb just because of common sense.
The tower 75 would be more than enough for the US60.
I'll tell you more, because of using the 75AX with 13x8 prop I had problems of prop ground clearance.
IMO instead of putting 91FX in it its better to start thinking about how to reduce drag with retracts.
I’d go with the tower 75 on the US60.
Its not that much sanding on the US60 compare to 4*60 its actually easier because of bigger and fewer parts on the US60.