You will need to swap the centre latch (held on with two screws) from the old to the new gearbox as it is slightly wider now. The deadbolt is also slightly wider so the deadbolt slot in the face plate might need filing/enlarging.
Surelock Central Gearbox Lock Specification:
Spindle to key: 92mm
Backset: 35, 45mm
Lever Lever or Lever Pad locking operation
1 centre latch,
The centre latch can be handed LH or RH by removing and turning it.
Click here to view "Backset" and "Spindle to key" measurements
Click here to view suitable Lever/Lever door handles.
Click here to view suitable Lever/Pad door handles.
Please check that these handles cover any existing screw holes in the door.