Locate X302, remove and put a crystal switch in its place, put the crystal that was removed (X302) on to the crystal switch's pcb, you need to obtain a 20 Mhz crystal and put this on to the second position on the crystal switch, when all is done you will need to retune your frequencies, tune for the old frequency bands first using the adjustments on the crystal switch's pcb, then switch to the new frequency range and adjust the trimmer to tune the new frequencies.

With the new crystal enabled these will be the actual operating frequencies

When the display shows 26.000 MHz it will be on 24.000 MHz.
When the display shows 28.000 MHz it will be on 26.000 MHz.
When the display shows 29.699 MHz it will be on 27.699 MHz.
(these assume that you have already done the IC mods to get down to 26Mhz, otherwise it will be the same as the lincoln/HR 2600 models)

MAKE SURE THAT THE CRYSTAL SWITCH IS WIRED CORRECTLY INTO THE SET'S PCB, ONE OF THE SWITCH'S OUTPUT'S MUST BE GROUNDED AND THIS SHOULD GO TO THE GROUNDED SIDE OF THE CRYSTAL'S OLD LOCATION, FAILURE TO DO THIS MAY PREVENT THE SET FROM WORKING CORRECTLY.