I have the next size up Tatone mount attached to a 2x4... slightly different arrangement but still just a 2x4

I'd use bolts and blind nuts, not screws, to secure the Tatone mount to the softwood. A dose of loctite wouldn't hurt either.

Prior to my acquiring my Tatone mount, I fastened a 46fx directly to a notched piece of 2x4. At high rpm the mounting screws began to unwound themselves due to the vibration. No amount of tightening or use of lock washers would keep them in place. A bolt, however, stayed tight. Hence my concern about the screws.