I'd post on the Harvest Forum. Lots of recipe and preserving experts there.

I recently read about those melons. I think I was reading on the Baker Creek website, or Seed Savers, maybe Sustainable Seeds. I was looking for heirloom watermelons and these came up in the search. I remember reading the reviews and there were comments about what each grower used them for... most canned them I think. But don't quote me on that, it was a few weeks ago.

Ok ok I will check that forum.

Before WWII, preserves were quite popular. Citrons were grown as preserving melons. You can also make pickles from them similar to watermelon rind. Easier to grow then watermelon. Usually just threw a few seeds in the cornfield. Think of a citron as a watermelon that nevers ripens. A watermelon picked before it starts ripening can be used as a citron.

Yes very nice looking melon and hardy! Just need to turn it into something delicious and good to eat.

http://clickamericana.com/recipes/condiment-recipes/citron-preserves-recipe 

I grew them last year. They keep for a super long time, but I recommend using them before too many months pass, if possible. I had some quite old ones that looked and tasted fine, but I think they went bad because they seemed to make me sort of sick (unlike a younger one I had eaten). Anyway, mine were too seedy to make using them for pies, pickles and preserves very easy, and they didn't seem as suited to sugary recipies as salty ones to me, anyway. So, I found out through experimentation that they make great water chestnut replacements in stir fry. Just cut up the interior and fry it with your stir fry. It tastes just like water chestnuts, to me. Be sure to add rice.

Yours in the picture don't look ripe, yet, though. You might wait until the tendril shrivels. They seem to ripen in storage, if you don't have time to ripen them on the vine, however (when they turn a lighter green).

I'm not sure if they're like water chestnuts before they're fully ripe, since I didn't try it, but they might be fully usable before prime ripeness.