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 1-1/2 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.