If you are looking for something useable and not something that will be worked hard every day you will be fine. For years we had an 8N with a loader run off of the test port. We didn't know any different, it worked just fine, and it was a lot better than a shovel. Make sure your pump is in good shape and go after it. I'd hook it up, run it a day good, and then change all the fluid. You don't know what's left in that system right now and you sure don't want to pump in a lot of water and leave it in your tractor.
All that said, throw your pennies in a coffee can and save up for a front pump. You will appreciate the upgrade and your machine probably would, too