दशग्रीवः ten headed, त्वत्सकाशात् being so, विधिपूर्वकम् as per tradition, संस्कारम् ritual of obsequies, प्राप्तुम् to attain, धर्मेण righteously, क्षिप्रविथौत्देल्य, अर्हति deserves, त्वम् from you, यशोभाक् you will attain fame, भविष्यसि by doing this

"Ten headed Ravana being so (knower of righteousness), he deserves your performance of his last rites as per tradition and righteously You will attain fame by doing this deed."