yeah. the Yakima Hullraiser Aero kayak racks will work perfectly on your setup. The j-cradle kayak rack design maximizes efficient use of your crossbars for a good configuration to carry all 4 kayaks including the Wilderness Systems Alto models.
by the way, if those 78 inch crossbars are Yakima round cross bars or Thule square bars then you can go with the cheaper priced Yakima 8004039 HullRaiser kayak rack model. It doesn't come with the universal crossbar adapter clamps / hardware but it fits Yakima Racks round bars and Thule square bars directly and costs less than the HullRaiser Aero kayak rack model designed to work on factory rack crossbars (as well as Yakima Racks and Thule Racks).
here is a good pic demonstrating how well 4 Yakima HullRaiser kayak racks work on a trailer...
http://www.orsracksdirect.com/trailer-kayak-rack-yakima-bolt-toploader-1a-raingutter-towers-hullraiser-kayak-carriers.html