The dt200 engine is a direct bolt in I know, I just bought 1 from another memeber on here. They are very rare sold in canada, austrailia, europe and south america. not usa. everyone knows they are rare too so they sell at a premium. I been looking for 0ne for 2 years. they also made a dt230 also not sold in us which also fits and i have heard a wr200 also but again they are very rare. pretty much any other 2 stroke engine can be made to fit with welding and cutting but it gets prohibitively expensive unless you can do the work yourself. once you get a dt200 engine your local yamaha dealer can not obtain the parts for you unless you know the part number and it happens to fit something else that was sold in the usa. Forget about the liquid cooled cylinder head and stay away from any big bore cylinder or stroker kits from trenga racing and most of vitos stuff unless you have lots of mechanical experience and a fat checkbook.
There is a guy close to me with an late 70,s yz490 motor in a blaster which is overkill, it took him a lot of work to make it fit and its not in my opinion fun to ride anywhere but in a sand drag race. Good luck to you PM me if you find one and i will help you as much as I can. I will start the rebuild on my dt200 engine soon. will post up pix when I start it.
