I didn't notice your reply few weeks back.
Magic Site Mod adds 24 Holy sites of various levels, many of them underwater. I'll update it soonish, and I'll change all level 4 Holy sites to level 3, so that each nation has at least one priest capable of finding them. Have you given any thought to this problem?
If you only use site numbers lower than 857, the two mods should work together without conflicts, even if we don't throw them together. How many sites, approximately, do you think you are going to add?