This is less a relish and more a pickle, I believe. It is basically a recipe for bread and butter pickles. Which are very tasty. So make them. They won’t last long enough to can and seal, more than likely.
Ethel’s Cucumber Relish
Slice cucumbers thin, add to each quart one teaspoon of salt. Let stand 3 hours covered with water. Drain, and for each quart of drained cucumbers add 1 cup onion sliced thin, 1 teaspoon pickling spice, 1 cup cider vinegar and 1 cup sugar. Mix and boil 3 minutes. Can while hot and seal.