I have several of these vats. The devs made it a little confusing. The bottom half uses the vat images from Buc's Den, whiel the top half uses the vat images from the winery next to Empath Abbey. Those are the only spawning pieces, and the center, either variety, does not spawn. You can only assemble what Loriel posted as an image. The pile of skulls is a different colleciton of items, and there are small edge pieces in addition to the 3 shown above; total if I remember correctly of 8 items in that set.