On a friend's GB36, with traditional davits, the lift of a 9 ft Whaler with a 6hp outboard was at about the limit. A heavier whaler like the 11 would require a better designed davit system.
I don't know the make of the davits, but their scantlings were considerably less than those of my own davits, that lift a 750 lb 12' RIB with a 40 Honda, but in order to do so, needed an extra brace added, to eliminate flexing of the bulwarks they were attached to.
I have also closely observed the use of Nick Jackson transom mount davits for heavier loads, and so long as you can find a location for the lift cable that is strong enough, they work well for loads up to 750 lb.
Having seen several collapsed swimgrids on GBs, both 36 and 42, I would never trust them to carry much dinghy weight, so the installation of a Seawise or Weaver system will require considerable strengthening of the swimgrid.