That would be fantastic if you could do the YZ-J tank onto IT-K frame test fit, GT43.
I like your idea of the IT200 tank too.
I went out today and had a brief look at the fitment of a 250J tank/seat on the IT490K frame.
I'm not much good at explaining things, so I took some photos of what I saw.
I briefly fit the shock and looks like it clears everything, didn't get a shot of that because the camera went flat.
With "J" sidecovers you would have to do some hacking and welding of new brackets.
And if it were me, I think I would probably cut the IT loop bar off the back of the frame to top off the YZ look.
All in all it looks do-able, but a bit of hacking and welding is needed.
There maybe something I have missed that may catch you out, but not sure.
Dont want to mislead you Nath into things going wrong.
If you decide to go ahead , hope you post a pic of it.