I also managed to place a Balance two router in this rack. But I had to bend the lateral retaining brackets downwards (into the recesses from which they were punched out at the factory). These seem to be new in the latest rack version and are not visible in the picture of risingconnection.com.au provided by @Marcus.
Meanwhile, I figured out, how the switch’s Inter-VLAN Routing for L3 routing should be used (i.e. the switch is routing directly between the VLANs it knows and is not sending all inter-VLAN packages via uplink to the main router to have the main router do the L3 routing, anymore (which is more time consuming)):
You need to assign a fixed IP-address to the switch for this VLAN
In addition, you need to assign another fixed IP-adress for this VLAN for L3-switching, too (must be in same subnet).
Both IPs must not be from your DHCP server’s dynamically assigned IP-range.
Example: