This section is from the book "Preserving And Pickling", by Mary M. Wright. Also available from Amazon: Preserving and Pickling: Two Hundred Recipes for Preserves, Jellies, Jams, Marmalades, Pickles, Relishes and Other Good Things.
To each two pounds of quinces use one pound of sweet apples. Pare and quarter the fruit, re moving all hard parts, then cut into thin slices. Cover the quinces with cold water and simmer until tender, then remove with a strainer.
Cook the sweet apples in the water that remains, adding more water if necessary to cover the apples. When tender remove with a strainer. Add the sugar to the juice in the kettle, using three-fourths of a pound of sugar to each pound of fruit. Boil until the syrup is thick, then add the fruit. Heat thoroughly, remove with a strainer and fill into jars. Boil the syrup until it is ready to jelly; pour over the fruit and seal.