Yes it can be done but you will need to know how to weld or know someone who can. The Y pipe will either need to be adjusted or fabricated. I have seen it done to a K7 750 with the 2x yosh Tri-Ovals. He said there was no change in driveability either.
I have 03 1000 titanium headers, on my 05 750 engine, 08 750 pipe, in my 04 600 frame and body. So yes 1000 headers from certain years will fit on an 600, and 750. Depending on the years. My 04/05, 750 will take headers from 01/03, 1000.