How to lift a large dinghy on a small boat is a problem.
I was in this situation when I was trying to find davits for my Boston Whaler 9" w/15hp to be mounted on my Cape Dory 28 Open Fisherman. The weight (250 lbs for the boat and motor, and 150 lbs for the davits) was not a problem, as this 7500 lb boat was designed to carry a large load in the cockpit. In fact, the extra weight helped to balance the weight in the bow (anchors, living quarters).
I finally designed my own and had them fabricated from 2.5" Sch 40, 316L SS pipe. The cost was less than a similar factory made unit and much stronger. I had the boat and davits for 6 years (1990-96), lived on it for a while, cruised the East Coast and the Bahamas.