Dragnlaw, 4.5 quarts of cherries, 1 cup of lemon juice, 2 cups of honey, cook it down into a puree, it made 13 1-cup jars. You may have to guesstimate the quarts of cherries to 1 cup jars. They are sour cherries, with lots of water in them. https://nchfp.uga.edu/how/can_02/fruit_puree.html
You can do the same thing with the plum puree. I have nectarine puree, green grape puree, black grape puree, strawberry puree...really any fruit that will work with the above recipe, fruits that go on sale. Right now I have 14 lbs of peaches ripening in the kitchen to dehydrate and can in puree form.