Wash rice; add the 7 1/2 cups (10 Japanese rice cooker cups) water. Cook rice; let stand for 15 minutes. Cut each block of SPAM into 10 slices. Fry SPAM slices to desired brownness. Place cooked rice in a large bowl. Combine 2/3 cup water, salt, mirin, and soy sauce. Sprinkle 1/2 of mixture over rice; mix well. Use remaining mixture for moistening the nori and knife. Place a sheet of nori onto a flat work surface, place musubi mold in the center of the nori. Fill musubi mold 1/3 full of rice; press rice down with inner section of mold. Spread ume on rice; place two slices of SPAM over ume. Add more rice to fill musubi mold; press down again. Remove musubi mold and wrap nori around the musubi, sealing edge with a small amount of the mirin mixture. To serve, cut musubi in half (for parties, cut into fourths). Garnish with furikake and benishoga. Makes 20 SPAM musubi.
Approximate Nutrient Analysis per musubi (using 1/2 the mirin mixture) :
390 calories, 11 g fat, 4 g saturated fat, 20 mg cholesterol, 550 mg sodium, 62 g carbohydrate, 1 g fiber, 1 g sugar, 9 g protein