First off my apologies to mark in not getting back to your original question.
Matt now I can answer for both.
First off the plastic wheels was not a problem to heat because the torch tip and plate being cut in front of the carriage would and should not heat up to a high temp, in a perfect world once the cutting has commenced there should be only residual heat left over on the immediate surface area.
Overall this little gismo was a failure and needed major surgery, the four wheel design just played havoc with steering and trying to keep it on a straight edge was near on impossible, the beam spanning from the center to the end holding the torch was to flimsy, it wanted to twist as the grip from the ali block was not sufficient enough. In the end I chopped off the wheels and tig welded two back on then I took ½ dia stainless steel instrumentation tubing, drilled a new hole in the block and affixed it to the torch end, it worked great after that.
Ironically my boss just loved the little thing and had the nuts to ask me to make one more for another quarry that we own, it was instantaneous the word B****cks fell out of my mouth and I concluded my sentence by telling him to go buy one the cheap B*****rd.
Happy days!!!!! Anthony.