Perhaps the new Marlin Builder tool might prove useful, if you're unable to compile your own:
I've just set Cura 13.06.5 to the sizes that you mentioned, and then scaled a simple STL to fill it, and it seemed to slice the file just fine.
Don't know. YOu have to try it. Dimensions are under "file" "preferences" I beleive.
As far as Marlin...
There is a new Marlin builder here:
It seems to be working okay now. If you have any problems send feedback! I've done some limited testing and other's have also. Not sure if it's ready for prime time yet.
Or you can read this and build Marlin yourself:
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