I fly both aircraft regularly,
It has always been explained to us that the 757 uses isolated left system hydraulic pressure and a dedicated DC powered Hydraulic pump to release the uplocks, allowing the gear to free fall.
The 767 uses an electric motor to trip the locking mechanism (uplocks)
As EXDAC has stated above, there is no mention of an associated CB for the 757 Dedicated DC powered Hyd pump.