Let me start off by pointing out that derailer tuning isn’t very cost effective.  One can save weight elsewhere and in other ways.  Also, a DA 7700 r.d. isn't the best starting platform, its quite old by now and heavy.  You’re better off going with a SRAM force or SRAM Red setup. 

I just happen to like this setup so I’m going with it.  I also enjoy learning the size of every bolt on every derailer and picking the colors so I love tuning them.  In a case like this Its more for fun so I don’t go too far out of my way to change everything and I surely don’t do anything that would reduce the reliability of the component.

First:  Start with a working derailer.  preferably something cosmetically ugly and cheap so you're not so hesitant to cut into it.

200 Gram Fatty
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Most people start and stop here with the jockey wheels.  There are a lot of these on the market and the prices can be quite perplexing.  I just went with a rather inexpensive one, no carbon wheels or ceramic bearings.  Still haves some weight though.
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As mentioned before, start with an ugly one.  Mine comes with some rock rash from the previous owner. 
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That way you’re not so afraid to drill into the face.  NOTE: Measure first before drilling. My holes are all off due to lack of time.  Most derailers are overbuilt near the face.  Taking away material there doesn't compromise the rigidity of the linkage.  Some people drill out way more aggressively than I did and It's all fine but It does let more dirt and grime into your torsion springs.  Drill at your own risk.

Pop the pivot bolt C Clip out and switch the pivot bolt for a nice Aluminum piece.  Then put the pieces back as they were, preloading the torsion spring. (This is the hardest part of the install)
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WHAM.  All that for 20 grams.
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But now it looks crazy like something straight out of Willy Wonka’s factory.
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Good places to get Aluminum and Titanium bolts, bits, and pieces are:

http://www.torontocycles.com/ and eBay

Or if you’re lazy, don’t care to learn anything and have money to blow: 

http://fairwheelbikes.com/

I didn't get every bolt.  Some of the stock ones are already the lightest possible.  I believe the most cost effective bolts to change are the pivot bolt, cable pinch bolt, and the cable adjuster.  Most good quality derailers nowadays come with aluminum limit screws already.