Ryan!
You might need to go a bit more than an inch! Depending on who the mfg. is and whether or not they modified the fender from the original, you actually only have about 8" to 8-1/2" of useable inside width on a KIT fender because of the way the fenderwell lip curls in at the top of the opening. The other thing is, if they are from molds taken from the original KIT fenders, then the overall widths are different left and right, and neither is a true 9". (Shameless plug, here: my 9" KIT-style fenders are a true 9" overall width, and they have the most available useable inside width at just a hair under 8-1/2")
It might be easier to
narrow a set of 11" wide fenders by about 3/4" or so (Doug Hodder posted an excellent tutorial, here, on how to do just that a while back!), or simply put 1/2" spacers between the wheels & hubs to push those tires out further to fill out the 11" wide versions ...

...
Hope this helps! Good Luck, and in the meantime ...
CHEERS!
Grant