I cut down my sons razor pro deck down to 17.5"...(he is only 4 yrs old)
I have a couple pics of the process i will post for you when i get a chance. Its real easy...just carefully measure and mark it out, then drill your new hole for your rear axle...to cut the deck the easiest way is with an angle grinder with a zip wheel (cutoff disc) and a die grinder w/ a carbide burr to round out the rear wheel slot. Then just some sand paper and a file to smooth it all up when your done.
...Or if you are lucky enough to have access to a machine shop...do it the correct way on a cnc milling machine.
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