Genuine Spoon Sports seat stays. As shown in the picture, one of the inside ears has been cut and extra hole drilled on bottom. Still in good working condition
From Spoon Sports site:
Aluminum side brackets for custom racing use only. Modifications may be required for installion. Not designed for direct bolt-in. Sliders and hardware not included.
Price from Spoon Sports new - $420
Link to Spoon Site https://spoonusa.com/spoon-aluminum-seat-side-stay-set-r-l-accessories