For anyone wondering what I ended up doing was setting up DNS entries for the different servers.
Externally, they all point to the same IP, internally, to the different servers.
As I get my hands on the devices with the old config, I'll update them accordingly.
Since it's all going off a single IP, the external devices which I can't updated would work just as well with domain.com as with server01.domain.com when it comes to the port forward externally.