Target engines:
* ProQuake [even the new Flash build, barring an impossibility]
* Enhanced GLQuake/WinQuake
* TyrQuake
* JoeQuake
* Qrack
* FitzQuake
* FitzQuake SDL if possible
Assessing the difficulty/planning:

I don't know what the qclib folder is, maybe it'll be obvious as I progress.
The rest of this at a glance looks straightforward and non-problematic.