Transparent VDOM w/ multiple subnets/physical networks

I have a situation where we are inserting our Fortigate 60D in between a customer's existing switches and their gateway. The gateway is programmed with two separate physical interfaces with subnet A and subnet B, neither of the networks have VLAN tagging. 

Is there any special configuration that needs to be done on the transparent interfaces in this situation, or can I just create four transparent interfaces [1, 2, 3, 4] and create policies only between interfaces 1-2 and interfaces 3-4 [port 1 is plugged into the switch for network 1, port 2 into the gateway port for network 1; port 3 plugged into the switch for network 2 and port 4 into the gateway port for network 2]