If this helps:

LT series has the Kanzaki K46 or K51 (wow that's tiny!)
LX series has the Kanzaki K62 (bigger)
GT series has the K71B (bigger than LX).
GX looks the same as GT, type not specified.

<http://www.stonehams.com/pdf/lt150trac.pdf>
<http://www.stonehams.com/pdf/lx280_289.pdf>
<http://www.stonehams.com/pdf/gt200trac.pdf>
<http://www.stonehams.com/pdf/gx300trac.pdf>

<http://www.deere.com/en_AU/equipment/cce/lawn_tractor/lx_specs.html>
<http://www.deere.com/en_AU/equipment/cce/lawn_garden/gt_specs.html>