Third stage:
-The larger fire allows for larger missiles (Isis II) with 0.53m diameter (one with Exocets, other with Isis)
-On the final design I think that Blackbuck will be credited as well for his assistance.
-I am not sure for rest equipment (sat-com definetely, perhaps some kind of TACAN), rail in bridge area etc.
-For propulsion I think twin 6,000hp-7,000hp for low speed and twin 32,000hp for high speeds.