So if you have this:
HQ LAN (clients 192.168.100.x/24) -> B380(192.168.100.1) -> Internet <- B210(192.168.1.1) <- Remote LAN ( Clients 192.168.1.x/24)
And you have set up a typical Layer 3 SpeedFusion VPN (so no NAT checked in the profile and no layer 2 configured), then each Balance learns about the LAN subnets at the other location automatically using OSPF (the B380 tells the B210 what LAN IP range it has and vice versa).
That means that network settings of the LAN clients at either location stay the same and when they want to route traffic to the other site, they pass that to their default gateway (the Balance in each case) and it forwards traffic for the remote site over SpeedFusion VPN (since it knows the IP address range that exists at the remote site from OSPF).
In short - it should just work.
Do an IPconfig on a device at both locations and check that in each instance the default gateway is set to be the Balance local to that device at the same site.