Its worth a try.

Maybe you should inbreed it and also cross it with the best of the others?

I just dont have any other plants that even come close to being what it is so I am afraid to do anything but inbreed it. So I think as long as there aren't any huge negative effects I should probably inbreed it to keep the vigor. Thanks

I've never worked with cucumbers, but Carol Deppe's book, "Breed your own Vegetable Varieties" lists Cucumis sativus as self compatible. If I understand correctly, flowers may be either perfect, or separate male and female flowers. It notes that in some modern varieties flowers may be almost all female. Since you have heirlooms, that shouldn't be a problem.

You should be able to inbreed it, but if there is a problem, such as male flowers developing before female ones are ready, then you might have to cross it with others, and then try to inbreed the offspring to get back the properties you want.

It is always possible that this isn't a new variety, but a different seed that got mixed into your package by mistake.