Nope, I am way wrong, what you are doing is right,
Some of the pieces are shaped the same so at first glance I thought we had the same mower but, after looking more closely at the pictures you have a different frame all together. It looks like your frame is different, enough so that I am not going to be of much help.
My motor plate does step down as your does just hard to see, but the rear portion is different, mine comes down further than yours does...
I sometimes have problems visualizing where the ride hight is going to be so the easiest way to see where things belong is to mount up the tires, put them on the axle and set the frame on top. that way you can see exactly where things are.
Where are you located ? Maybe I can run it over and show ya how mine is done ?