Bordermanager 3.5 server on Netware 5.1 providing firewall and proxy
services for users on internal network. This box is also acting as the
Master VPN server with multiple site-to-site VPN links to BM 3.5 slave

Primary Goal
Replace the existing Bordermanager 3.5 master VPN server hardware with a
new server running Bordermanager 3.8 on Netware 6.0. It is possible to
have both servers online during migration. Must minimize disruption to
firewall, proxy & VPN services.

Secondary Goal:
No changes (or minimial changes only) to the slave servers running BM
3.5. (These boxes are located in remote areas with minimal support
available onsite).

Best approach to meet both goals?
Will the 3.5 slave servers communicate with the new 3.8 master server?
How much can be preserved and how much should be recreated?