Hi,
The answer very much depends on what you wish to achieve. From HSRP point of view at vlan 56 the address that matters is the virtual address you assign by "standby ip" command. Ie should you prefer to keep your default gateway address unchanged you assign it as standby (and assign new addresses to vlan56 in both MSFCs), should you like to keep of interface vlan56 address unchanged at MSFC1 you should assign different address as stansby and then change default gateway. The first example may look like this:
MSFC1:
interface vlan 56
ip add 156.175.20.2 255.255.255.0
standby 1 ip 156.175.20.1
standby 1 priority 10
standby 1 preempt
standby 1 timers 5 15
standby 1 authentication cisco,
MSFC2:
interface vlan 56
ip add 156.175.20.3 255.255.255.0
standby 1 ip 156.175.20.1
standby 1 priority 20
standby 1 preempt
standby 1 timers 5 15
standby 1 authentication cisco.
For the case you would like to keep the ip address of vlan56 unchanged you just change the 156.175.20.1 for 156.175.20.2 and vice versa.
Best regards,
Antonin