Weight doesn't matter on a track bike because you can easily get below 6.8 kg without trying, and then you have to start adding weight back on somewhere.

I've never been a weight weenie and had some of my best results on an old steel pinarello frame that they didn't even weigh at nats-- the official picked it up, looked at me and chuckled, and then moved it onto the track. I've had a couple of bikes since then that I had to add tens of grams to (electrical tape was enough).

If you're going to play games with where you put the weight, minimize what's near the OD of your wheels (rims, tires). If you're still under 6.8 kg, put any extra weight high up on the frame (though it will hardly make a difference out of the total weight or angular momentum anyway).