A simpler way would be to go into the tooltable and add 2 user fields ie XProbe and YProbe and make these integers, you can then call these like
local xpos = mc.mcToolGetDataExInt(inst, selectedtool, XProbe)
local ypos = mc.mcToolGetDataExInt(inst, selectedtool, YProbe)
mc.mcCntlGcodeExecuteWait(inst,"G90 G53 G0 Z0.0 \n X"..xpos.." Y"..ypos)
obviously you would have to populate the table for all tools which should be straight forward.
DazTheGas