Years ago I converted a GURPS campaign to Arcana Evolved, a 3.5 variant by Monte Cook. What I did was give clerics access to some force spells (sorcerous blast, wall of force) and said that they did holy damage (radiant today). However, they only worked against undead, demons, and such.
The direct damage was simpler and access to some of the other spells allowed for walls of force keeping undead out.
The direct damage was simpler and access to some of the other spells allowed for walls of force keeping undead out.