Sachs made a triple top-pull braze-on that was pretty light. I believe it is called the NEOS. It can be tuned with aluminum bolts and a lightweight clamp - like a BTP.
I have one of those, in the picture it has an aluminium mounting and clamping bolt, the rest is stock. I would say you could easily save about 10 grams from stock by replacing all the bolts to alloy and drilling it a bit as the cage and arm are quite beefy, without really compromising much.
There aren't to many top pull derailleurs, but there must be something lighter then this one?
I still have plans to try and convert a record fd to top pull but it's not very high on my priority list so I haven't got the time for it yet.