Not a solution I'd do myself, but I can understand where you're coming from. Here are a few observations, based on my experience with Kato davits
on my boat.
You'll definitely need cross bracing near the end of the arms, maybe 3/4 of the way out. The whole thing needs to be quite rigid, because it will be subjected to a variety of up and down and sideways forces.
You'll probably be using 4:1 and/or 6:1 blocks and tackle to hoist the dinghy. The topmost blocks could be shackled to eyebolts installed at the ends of the arms. You'll need to haul the dinghy up as far as possible to avoid swinging. When the dinghy is up tight in the blocks, the braces you show between the uprights and the horizontal arms look like they may interfere with your dinghy.
The uprights on my davits are attached to the pushpit. The base of each is attached by a base flange, through-bolted through the caprail and fiberglass deck
. A SS strap was added adjacent to each upright from the top pushpit rail down to the inside of the cockpit
to add bracing to support the pushpit.
Finally, it helps to cross brace the dinghy itself. I have two nylon webbing straps with ratcheting mechanisms for tightening. One end is attached to the base of a pushpit stanchion, and the other attaches to the dinghy with an "S" hook. The two straps criss-cross each other and serve to pull the dink in toward the stern, as well as keeping it from swinging and swaying. You could do the same thing for cheap
with polyester line and a trucker's hitch.
Hope this is helpful.