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New Dura ace calipers come pre bled. When you’re ready to install it carefully twist the black plastic cap out of the calliper to expose the hose port. If you do it carefully you might get away without needing a bleed, though once it’s installed you might want to tap the caliper and hose gently, so any small bubbles go up into your lever reservoir rather than get stuck in the calliper.
If you ever want a like-new rear caliper, let me know I’ve got one sitting around...
RX4s you'd need hope fittings to go with but they are included, whatever shimano you go for will work, you'll probably get away with just unscrewing it and screwing the new one in but wouldn't hurt to have the correct olive and barb for your hose to hand just in case.