How will he be 50lbs?? Really. If silva drops to say 178 then fight night he will be no bigger than 190. Gsp walks around at around 190, come fight night he will fight around 180.
You are most likely wrong.
Some fighters put up to 45 pounds on before fight time (Tito Ortiz)
So if Anderson Silva went down well below his normal weight he could probably put on 20 pounds or so and be around 198 come fight time.