When I read the Wiki about ruins, of all the ones they describe, the largest are chunk sized (16x16). In my new world I have found one that is over 200 blocks in both dimensions. Thic would seem to be over 200 chunks. Does this mean that there should be over 200 treasure chests in it? If so, I'm going to be searching a lot.
On that note, I've not explored but one small ruin in another area which actually extended above water and, consulting the Wiki, seemed to be a mossy_2 type. Chest had wheat, bread, and a treasure map.