A 2000 loader currently on a 606 WILL NOT fit onto an 806. Front mounts are entirely different. Rear axle mounting method is entirely different , plus frame is shorter. That being said , if you can build front mounts that are like the ones that are required for 806 and can extend the subframe and build the rear mounting for the 806 axle , then you could mount it as easily as if it was built to mount on the 806.
I have Operator's Manual with diagrams of all the mounts for various tractor models. I have them scanned and can send them to you if you like. Also pictures of factory mounts of a 2000 on my 856. I've sent this info to others who wanted to modify a loader to fit some other tractor. Incidentally, I have a 2001 loader on an IH 504 that uses same mounts as a 2000 on a 606 .