1. I'm normally all for cutting up a machine and going crazy with it, but unfortunately the 200x frame is pretty puny and the suspension won't take much more than its already got. ..
http://www.3wheelerworld.com/showthr...now-what-to-do . it's a small diameter frame and if you stuff a large engine in there it'll Crack apart. But it would be sweet to see a peppy liquid 2 stroke in it! It's been done before but that's because it'll actually work. Something like a cr125 engine could make a 200x a zippy machine without adding 40 pounds. If you really want a sled pulling rig maybe start with a bike and convert it to a 3 wheeler.
2. If you want a hard tail why don't you get a hard tail? Ie, 185, 200, something like that. They are far more common than a 200x and can often be picked up free cuz people are sick of looking at them. The 200x was cool because it has suspension, so please don't do that.
I understand the desire to do something original, but don't be hasty. Think it through and have a good end goal. A sled pulling trike made from a gsxr or something could be sweet