I believe that both of these holders were originally designed for dry plate. The 5X7 is a dry plate holder, with film sheaths for 4X5. One could easily shoot film with this holder, but obviously its more convenient to use a more modern film holder. You could shoot wet plate with it, but again, its not ideal. One would have to be exceedingly careful while handling the plate. I have shot wet plate in a dry plate holder for 8X10, and while it works, its quite cumbersome. Your 8X10 plate holder would be much easier to adapt to wet plate work, and would be a suitable working wet plate holder for use with a semi modern 8X10 camera with a spring back. You should just give everything a couple coats or varnish or poly, so the silver nitrate won't destroy the wood too quickly. This holder looks like it has seen better days, but should still hold some value as they don't come up on the used market too much.