I need to run an ioquake3 server under protocol 43 (quake 1.16), anyone know if this it's possible?
As far as I am aware no code or documentation of the past Q3 protocols is publicly available. Not currently possible.
This is also addressed in our wiki: http://wiki.ioquake3.org/Sys_Admin_Guide#Using_Old_Versions_or_Protocols
The majority of mods built for Quake 3 1.32c work fine with ioquake3, but sometimes we get asked to help with NoGhost or other mods that require versions of Quake 3 prior to 1.32c. When the source code to Quake 3 was released it was for version 1.32c which is why ioquake3 increased the version number from there. We did not receive the source code for versions prior to 1.32c and there is no way for us to go back to 1.16n or other old versions. For the very few mods that require 1.16n, there is no way to make them work on ioquake3.