Hi Frank...
I hold that doing it your way, which is neat, has two shortcomings:
1) when you hog out the beam, you are creating a potential for stress at the edge of the cut.
2) you are remo9ving material from the place (under/over the engine) where the most mass is desired.
Also, I have found that installing the 1/8" pads onto the mount also allows for more adjustment with the tank.
BTW, the Moonies make some pads that are 3.16 thick, allowing them to be drilled and tapped.
Just thoughts, echoing some thoughts of Big Jim Greenaway and Winfred.....