Also, if you do acquire a free dish and it's not a one-piece type, (I don't recommend real OLD fiberglass dishes for newbies, though there are some good ones) do NOT assume that it was put together correctly by the first installer. ALWAYS measure and check ALL settings, bolt together edges, ect. that they are done correctly, and it's put together right.
We can usually figure out the maker of a unmarked dish if we have enough good photo's of it and the mount. Once we know that, it's likely we can find the original specs and you can make sure it matches.