Just to clarify your question... you wish to connect to the instance on either server without the need to specify the Port Number?
In that case, did you check if the instance name is added into your SQL configuration manager?
- Open SQL Configuration Manager
- Expand "SQL Native Client Configuration"
- Select "Aliases"
- See that if the instance that you wish to connect exists, if no, create the alias for the instance
Hope I do answer your question...