Just saw this post for the first time today. I like the YZ465 and the IT465s out there. That pipe is from here http://www.x-tremevintageyz.com/
I myself have a 1979 Yamaha IT175 (my first bike) and it has been ridden hard. Looks different from these pics.
Here is my 1981 Yamaha IT465. Its ugly and i plan to keep it that way. Its going to be my first hill climb bike. I plan on pipe, head porting, head mod(Eric Gorr, he has been building them since they came out), 10 inch extension on swing arm and some paint. I will post when i am done.