The 35670A/U-AX4 rack mount kit uses the 5061-8064 kit and is for both newer and older 35670A units.  The 5061-4846 and 5062-4841 kits which show up on the Find-A-Part web site are for spectrum analyzer products that are supposed to use the same frame, but they are slightly different.  The flange and dress panel are different.  Contact Agilent support to get a copy of the 35670A rack mount installation note that provides detailed drwaings of the rack mount hardware.