Problem Solved! .......... And a new problem arises
I added the stick-on rubber feet to the Mendel and they raised it just high enough for the Z-screws to clear the bench. I also found that using lock washers on each side of the Z-axis bearings solved my problem with the washers contacting the mounting screws. This means that I am good to go for the rest of the build.
Or it would if I hadn't encouontered another problem as soon as I moved on. The Z-axis belt proved to be too short, even with the tensioner in the loosest position (as these pictures show. I obviously messed up my parts order somehow so I will take a look at the bill of sale to see where I went wrong.
This doesn't mean that I am stalled again. I should be able to proceed with everything else while waiting for the new belt to arrive. I now have all the motors installed and I have the x-axis moving smoothly (by hand). I think that the next step is to install the electronics and the build table.