I'm assuming the spec you're looking for is the maximum weight allowed. On mine, there is a sticker on the front cross bar that says "Maximum weight 175lbs evenly distributed" and then repeats it in kilograms.
I've got a 2 person Perception kayak (
http://www.perceptionkayaks.com/acadia-ii-14) it's pretty heavy but still just 82lbs, so two kayaks on this rack should be no problem. It's the actual space up there that I would be worried about. For two kayaks I would consider getting rid off the factory cross members and installing a pair of Yakima or Thule cross bars that not only give you a completely flat surface all the way across, compared to the slightly bent factory ones, but also give you more room since they extend beyond the side mounting clips.
The aftermarket cross members mount into your existing Toyota roof rack rails.