For an older guest release that does not recognize a configured DE500, the DE435 is the conservative first alternative.  Historical guidance used the DE435 for OpenVMS releases before V7.2 and Digital UNIX releases before V4.0, but those exact cutoffs were not revalidated across every kit for Avanti 5.1.0.  Treat them as troubleshooting history rather than a complete compatibility boundary.

Consult the network-driver documentation for the installed guest release, verify which adapter the guest actually enumerates, and validate bidirectional traffic before retiring the previous configuration.  See OpenVMS Specific Notes or Tru64 UNIX Specific Notes for the supported guest-family boundaries.