The big wheel KX,RM,CR, etc, including the 100's have 19'' fronts and 16'' rears. The "small wheel" or regular versions have 17'' fronts and 14'' rears. You can use KX80 wheels from the larger "big wheel" version. The KX100 frame geometry may be different, I'm not entirely sure though.
I stole this from a quick search,
If you convert it to a big wheel bike, you will also need to put a larger sprocket on the rear wheel. The difference between an 85 and 85L is about 5 teeth. You will alslo need a larger chain to match the extended length and larger sprocket. (In addition to the longer swingarm)
Check into the cable lenghts too!