It's my lucky morning! I hit another survival island seed, LARGEBIOMES again... Several hundred clicks to the south, just under the sand, under the water, is a stronghold that eventually connects to a huge abandoned mineshaft system, so, you could probably dig down to about 35-40 and tunnel under the seabed until you reach the stronghold.

UPDATE: I've done some survival on this one and there is a spider dungeon on the west side of the island about two or three blocks underneath the surface. In my opinion, this is the best dungeon type to have in survival island seeds due to string for beds and fishing rods!

This seed was generated with version 1.6.2, Rei's Minimap, Forge, Inventory Tweaks, Optifine, and Sphax BDCraft resource pack - I've heard that some mods can affect the seed, so let me know if you find something different with other mods installed!