Gary, the 1-7/8 nut may be the cause of the play, it has to be tight....REAL tight.

Under the bracket that you are trying to get off there is a tapered washer...only way I can explain it........try getting it off first, a couple of screw drivers and walk it off, This is a salt water motor Right?

Most times if the motor shakes back and forth (like the upper motor mount is gone) the 1-7/8 nut is loose, I use a 1/2 inch air impact and hold it until it stops turning to tighten this nut.