Layer 2 LTM cluster setup in 11.4.x

OK, I'm not sure I understand the full picture on how this works but perhaps that's not necessary. So, if you use a dedicated VLAN and some nonsense addresses between devices you can use network failover with HA-groups or all the failsafe features. Alternatively you could drop even those addresses and use the serial failover cable instead. Regardless you'd need to create the relevant device group and trusts but this can be done through the management interfaces. Does that help?