I will try to get the exact measurement for you this weekend, but I clear the door buy about 1/2" I believe.
As for the trailer I believe it is the leaf spring design, but I will check that too. When I got my boat there was some discussion on here as to whether there was any difference between the torsion and leaf spring design and I think the general agreement was there wasn't much difference between the overall ride height.
I will look at the tower too and see if adjusting the retaining cable will allow for any further drop.
Like I said I was very skeptical when we bought ours but I was very pleased with how easily it went in with just removing the board racks and changing to a drop hitch once back at the house. The only thing about changing to a drop hitch is the Fulton dolly will not go low enough to get the tongue onto the drop hitch so I have to use a jack to change hitches. Currently I am looking into changing the factory dolly thing and either getting one with a smaller wheel or just a pedestal one so I don't have to go get the jack out of the garage.