Do not, under any circumstances, type in "no failover". You will be in a world of pain.
Second thing, make a backup of the config.
Plug in all the cables on the replacement unit, make sure all the interfaces are up, and put in the failover config as you have noted, and the new unit will get its config from the current unit.
interface gig0/0 no shut failover lan unit primary failover lan interface failover GigabitEthernet0/0 failover key test1234 failover link failover GigabitEthernet0/0 failover interface ip failover 10.148.255.6 255.255.255.0 standby 10.148.255.7