Jones looks bigger then everyone he fights. It is all because of his extremely long legs and arms. Look at his torso, Silva actually has a longer torso, his hips are noticeably lower then Jones' but his shoulders are only slightly lower. Thickness wise Silva looks to be thicker as well. The only significant difference is that Jones' legs and arms are 3-4 inches shorter(and skinnier as well).
Jones' frame and reach do give him advantages, they are pretty much what makes him such a special fighter. All I am stating is weight wise these guys aren't that different whereas some people believe there would be a 20-30 lb weight difference between them on fight night.
This fight if it happens comes down to skill and natural abilities. If Jones wins it is because of his freak body build and wrestling. If Silva wins it is because of his striking, experience and jiu jitsu.
You know that those ridiculously long limbs weigh something right? He does have about 20 pounds on him and his freak limbs and 2 or so inches of height are bigger advantages than having that difference in thickness alone. I'd trade the moderate boost in knockout power for a foot of reach and exceptional leverage in grappling.