I have the Edson davits, which mount similar to yours. The below link is a useful guide, but not completly how I mounted mine. I used a 12x12 backing plate and 1/2 inch bolts. A caution would be to not have any balsa core under them, the load on the bolts is quite heavy. I put a spreader bar across the ends and a second one bacl near the cleats. I also had to have 8 inch high "I beam" extensions made to reaise them. For the dinghy I secure the painter and a stern line to the quarter cleats (sweated tight) and run lines diagonally across above the dink. I am carrying a 9 1/2 foot Nautica RIB with Tohatsu 9.8 four stroke. This is for sheltered and coastal waters, for off shore my intention is to put both boat and motor on deck. So far this has been fine for several trips between Maine and the Keys, home port near Annapolis.

http://www.bbyachts.com/uploads/files/2009-06-17_Edson_Dinghy_Davits_on_Alden_54.pdf