Combine first 5 ingredients; stir well. Add steak and shrimp; cover and marinate in the refrigerator for 3 to 4 hours or overnight. Cut a thick slice from top and bottom of pineapple. Quarter pineapple lengthwise; remove rind and core. Cut inot 1- half inch thick chunks. Set aside. Remove steak and shrimp from marinade, reserving liquid. Alternate steak, shrimp, pineapple, and mushrooms on skewers for grilling. Gradually stir cornstarch into reserved marinade in a small saucepan; cook over medium heat, stirring constantly, until thickened and bubbly. Grill kabobs 3 minutes over medium coals; turn and brush with marinade. Grill 5 minutes or until desired degree of doneness, brushing with marinade as needed. SOURCE: Southern Living Magazine, sometime in 1980. Typed for you by Nancy Coleman.