Alec,
That looks like a standard investment cast seat lug with his logo cast in, and a pair of flat seat stay plugs mitered to fit directly up to the binder area. Sinple and interesting approach requireing mimimal work.
Brian Baylis
La Mesa, CA
I always thought the seatstay/lug/clamp on my 88 mondonico was very clean, simple and elegently done (photo on link below). Not sure exactly what style or who makes the lugs, any info would be appreciated. I believe this frame was one of the first batch after Mondonico left Guerciotti in 1988 but bike history always seems a little hazy so who knows for sure.
http://imagedeposit.com/