Yes you can upgrade some older basestations to become a FSII-base station 
See section 12 of the attached on how to upgrade a FreeSpeak base to FSII base  PLEASE NOTE THE FOLLOWING  

a)     You CANNOT upgrade a DRAKE Freespeak Lite basestation – If the FS basestation does not have any Partyline XLR connections on the rear then it CANNOT be upgraded to FSII Base   

b)     You can upgrade a FreeSpeak10 base to FSII-base  

Note(i) you cannot mix old FSPB units and New FSII-BPs on the same basestation. You cannot mix old PD2201 antennas and New FSII-antennas on the same basestation Only new FSII-BP and FSII-antennas will work on a FSII-base 

Note (ii): Not all FreeSpeak-Base or Cellcom-Base units are able to upgrade to make use of FreeSpeak II Transceivers. 

-         If your base currently shows 20 Beltpacks on the blue menu display then you will be able to upgrade.   If the base becomes unresponsive after pushing the FPGA file using the Config Editor, try pushing the file using the xilinx method.  see instructions below.

-         If your base currently shows only 10 beltpacks on the display please check the serial number of the basestation o   If the serial number is less than (below) 1761. Then it CANNOT be upgraded
 

Note (iii): You also need to upgrade your PD2203 splitter unit. This upgrade is h/w modfication. you can send your PD2203 to a Clear-Com service centre for a FOC upgrade. You only need to pay for transportation & any customs cost to/from the service centre