Wow, I "sorta" got what I wanted, I got a lot of comments, and confirmed that I need an expert on hand whenever I do this!
In some ways it feels a shade simpler than all this, so I'm not sure what I'm missing.
I have an entire second HD that except for a few misc backups, was purposely not used so there's your second "clean drive". Then you/we/techie just flips which is which and loads Win 9 when it comes out later this year.
I think I'm seeing technical drive letter problems, but does that stop everything from loading? Can't you just manually navigate to the old C/User/Desktop/Shortcuts and double click them and let them load? Or do they all break because of that drive letter problem?
My broad goal is to treat the new drive like a semi-fresh primary drive just like a new computer with arguably mixed strong/weak hardware, and the OS will never know and never care. Then limping along a little, I manually can go back and look and say "Oh, I had that and that and that", without guessing or running two whole comps on my desk.
I really tried hard back in '06, to plan for the future, so there's say a 1 in 3 chance the hardware will run Win 9, then you just flip the drives, yay it's a (now slightly aging) Win 9 comp, and off we go.
Does that make sense to anyone?