If the DEC bridge is public, the host BIOS will check it all all the devices behind it, and perform all the configuration necessary. This is a standard process that most reasonable BIOSs handle adequately. If this happens, then do not change the configuration or the bridge or the devices behind the bridge. The placement in memory has been chosen to coexist with other devices on the host, and changing things can confuse the host operating system or the motherboard.
If the DEC bridge is private, it and all the devices behind it must be configured by i960 software to be used. All the devices behind the bridge must be assigned address space as with any other device, with the extra restriction that devices behind the bridge must go in a single region. The region may have holes in it, but other devices not behind the bridge may not be mapped in that hole.
The bridge base and limit registers are then configured to describe the range large enough for the devices, and the range then placed in the address space of the bus that holds the bridge.