6-ply. Wouldn't surprise me if it is really heavy. Should be great offroad, but will probably do weird things on pavement, as most aggressive tires do.
If you do the math it's about a half inch shorter and almost an inch narrower. Neither of those factors should be an issue, except your rim may be a little more exposed than usual. The stock rim is 2.5 inches wide and most 110/100 tires call for a 1.85 or a 2.15 inch wide rim. It will probably fit but may not be ideal.
The 6 ply will probably make the sidewall a little stiffer so the bike will turn quicker. I installed a Kenda Big Block 140/80-18 on my TW and it steers so much faster now with the stiffer sidewall.
If you do this make sure to take pictures and post results. It looks like this tire will have some serious bite off road!
Current bikes TW200 * R1200GS ADV * R80g/s * KLR250 Miami Vice Edition * Hawk GT - For sale!
The tires do look pretty aggressive for the road but I thought because of the DOT rating someone may have tried them.