I'm looking over our old WFUT code base and it seems that most of the work in porting it will relate to the change from vertex animation to skeletal animation after UT 99.
UDK has a lot of UT classes which you are allowed to use as a base in your games, many of which are just improved versions of previous UT 99 classes. You can also move up the hierarchy and subclass more general classes (PlayerInfo instead of UTPlayerInfo, for example). For WFUT, it would be much simpler to subclass UT stuff, although I would end up with a lot of cruft such as vehicle code and whatnot.
One thing I hope to do is implement a proper grapple. I always hated the translocator. While UT can be a fast paced game, I am wondering whether I can get close to the same feel of the Q2/Q3 WF grapple. I'd love to see the WFA grapple code if that is available...or at least get some pointers from someone (Inf, Zith?)