Can’t think of any Church guild specifically either which would be currently active, although there is Light/Holy ones, such as the Gallant.
For both i can recommend Assemblage of Uld. Even not a church guild, the motivations of a Dwarven preacher can align too, i can see. Such as keeping artifacts from falling into the Hands of Darkness. The Engineer is more clearer, too.
Still the Dwarf may be kinda part of the Church organization IC too, you know. And perhaps being in the Assemblage can be his mission.