C-weed

Hello everyone,
I've had a SH for a couple years, but just starting to work on it.

I am having some difficulty with a rear wheel swap, and I am hoping that you gurus can help me out.

I bought a white CBR900 (i think) 6-spoke rear wheel in the hopes of swaping it out with my black 3-spoke OE wheel.
Today, I picked the wheel from getting tire mounted, swapped out the cush drive, and when I mounted it, I found that there seems to be a little too much gap.
I measured the wheel hub, I found that the SH wheel was 6" wide, while the CBR wheel was 5.25 (or 5.5?).
I have searched around here, but was not able to find what I wanted.
Did I get the wrong wheel?
Can I use additional spacers? Where would I put them in? (I have a .5" spacer, but i think i need another .25".)

Any help is greatly appreciated!!

C-weed

Think I have finally figured it out... after a sleepless Sat night =(
The guy that sold me the wheel told me it was off a 900rr. I am guessing it was off a cbr f3 (which is narrower?)...
Can anyone confirm?

Can I use spacers to somehow make it fit?
or,
do I have to pay a few more $ to get the tire remounted?...

The hunt for answers continues...