There are no "boat" studs, a stud is a stud, available at any automotive supply store. Or you can buy them from a marine dealer for 3 times the price.Thanks for the help. Certainly didn't want to break them, nor did I want to put the "wrong" non-boat ones in.
Most carb studs are 1/4-28 top thread, and 1/4-20 bottom thread. You can use threaded rod, and cut to suit too. Take two of the nuts that came off, and jam nut them together, and remove. If you use threaded rod, you might want to use some lock-tight(blue).