Take the ends off and check out the insides. These look like they are wet exhaust manifolds, the fitting in the front and back is the clue. They can/will rust out or get thin spots from the water and exhaust gases/deposits. There can also be a whole bunch of scale on the inside and once you clean that away there may not be a lot of manifold left. Although looking inside the ports of that one, it looks pretty good.

Got nothing to add about using them as turbo manifolds but it is an interesting idea.