Can I convert my Xoom 3G firmware to Xoom WiFi or otherwise use the WiFi version of Jelly Bean?
Yes, you should be able to install a wifi only rom manually, I`ve just gone to ICS with 3g and its great. 

found these links useful:

http://www.youtube.com/watch?v=BfHwd2Nxw1U

http://www.icsforums.com/forum/showthread/6398

http://forum.xda-developers.com/wiki/Motorola_Xoom

hope this helps