I'm old, if not old enough for Oly <G>; the oldest Bluejacket's Manual I have dates to 1919, a good long time after Oly. But, redial davits have to spin.
As you surmise, you spin them out one at a time. You lift the boat out of its chocks, rotate both davits aft or forward as far as you can, until one end or the other clears. Then you reverse one, which sets the boat at a diagonal between the davits, and keep rotating until the whole boat is over the side.
Just bashed through some online photo references, which show all sorts of spars on either the fore or after davits (and both). None of those look long enough to be a strongback to gripe any of the boats to the davits in a 'swung out' sort of way.
So, I'll guess that what is represented on the davit tops are stowed awning poles--which would be un-bent and stowed before using the davits. If they are not awning poles, then they are "gin poles" used for getting inboard & nested boats moved to where they could be hoist out.
I'd wager that boat tackle was only rigged on the davits 'to need." Probably only a light line passed through to control the davits, and keep them from swinging in the wind.