Cut plums in half. Remove and discard pits.
Bring 2 cups sugar, orange rind, and juices to a full rolling boil in a Dutch oven, stirring constantly, 4 to 5 minutes or until sugar dissolves. Reduce heat, and add remaining 2 cups sugar, plum halves, and raisins; simmer, stirring occasionally, 1 hour and 15 minutes to 1 hour and 30 minutes or until thickened, skimming off any foam.
Pour hot mixture immediately into hot sterilized jars, filling to 1/4 inch from top. Remove air bubbles; wipe jar rims. Cover at once with metal lids, and screw on bands.
Process in a boiling-water bath 20 minutes.
Note: Store unopened preserves in a cool, dry place up to one year.