I have a brand new in the box set of Marland Enterprise Corp, Seattle that are rated for a 175-200 lb dink
This sorta looks like your photo , but I cant be sure..
Box shows an eight ft GRP sailing dink dink in the water. hooked up.
I wont break the set to sell just the mount arms and their swivel brackets , so for $ 200. its all yours , plus shipping to you.Not cheap but antique is hard to find new.
On close inspection my set looks far more robust than that mount , are you sure its not for a swim ladder?
My set is to be mounted on a swim platform and in addition to bolts require the platform to be chiseled for added support.
They have a transom bracket also so these arms and mounts could be correct , it must be able to accept at least a 1/2 inch fitting.
If you need a photo let me know.