I haven't heard of Grands being certified on floats - and to be honest I'd be a bit surprised if the 8000 Wips could be. The 8000's don't have an abundance of bouyancy aft - even on a short Caravan you often get wet feet loading guests when approaching gross - on a grand with the door further aft the question would be how far up your body would the water get. My suggestion is that if you can find a grand on floats call the owner and ask.
One of the features that Wip is talking about with the 8750s is more buoyancy aft - I suspect this was added as much as anything else to allow the floats to be certified on the grand.
Also, I don't believe that pods have been certified for operation with floats either. There is a huge amount of volume in the float lockers, however the opening size is limiting for large items and some water always gets in.