I will soon be replacing an aging NW60SP5 server with new hardware using
the Migration Wizard. All five servers in our tree run NW60SP5 and an
OES upgrade is not being contemplated.

A few questions:

According to the docs, the migration can fail if the destination server
runs eDir 8.6.2, but it's OK if the source server is at that level.
However, NW60 servers should be upgraded to 8.7.3 anyway. Is it better
to bring all the servers up to 8.7.3 before the migration or wait until
after?

The server to be retired does not hold the master replica, but it does
host the organizational CA. Better to update to 8.7.3 before the migration?

Thanks.