Years ago I set up a 16/1, my cement pad was 6x8x2 feet thick.  I used 5/8 j hooks x14 inches long  in the cement.  I discovered I was shaking my neighborhood when running.  I added 1 inch thick rubber horse mat under my engine/generator frame.  It helped but still thumped,  running 1 time it started making a different noise.  I found that it broke 3 of the 5/8 j hooks.  I ended up calling a special vibration isolation company, after a bunch  of questions including the engine speed. They set me up with special mounts  that corrected all vibration problems.   The only thing is the total frame/ engin assembly needs to be able to move 1 inch in any direction. So keeping things flexible was key.