The previous owner of my car fashioned an S-shaped clip that is inserted between the outside frame rail to keep the top from sagging. It's hard to insert and not very elegant. What was used when the car was new?
Vince, I checked the operation on my top irons which is the same as yours.
In your picture, the right arm rotates until it contacts the machined shoulder on the left arm preventing it from rotating further. This is a slight "overcenter" position built into the overall movement. Check to see if the right arm is registering all the way to the stop position on the left arm. If not, check all aspects of the top irons for complete travel.