Picture is a bit deceiving, and spacing of the blocks is not as is, it was the first bit of nylon I lifted !
There are 10" between the end plates, I will space the blocks about 5", with the limit switch's there will be about 4 1/2" travel.
Arvidb is right the Y rails are the weak spot in my machine. I have suport blocks already made up for bottom and top of the Y rails. Don't intend fitting them until I have everything where I want it.