You'd be money WAAAAAYYY ahead by just sending your carb and head to Ron at RB-Designs. You may not even need a 144 kit if you do those mods. The Gas Gas is fairly "loose" on it's squish band set up, and he cures that, which gives more power, better fuel economy, and easier jetting. That mod is only $75. Frankly, I don't think he's charging enough for it for what it does.
That would be my first step to test the waters. Then send him your carb. For $165 he puts a wing in the exit, cuts the slide, mods something in the passages to make your air screw actually do something tangible and rejets it. That's a lot less work than shoving a 200 engine in your frame, and you'd probably like it better anyway, 'cause that 200 needs the same stuff.
Check out his site:
www.rb-designs.com