360 manifold. Same number continued to be used on the 360 after the 340 was discontinued.
The 340 (and then the 360 without air injection) manifolds had individual exhaust ports, the common center port you have pictured was a 273/318 thing (I'm guessing that manifold was on a 340/360, you can see the carbon witness marks from the port mismatch).
Hint- 340s used a flat exhaust pipe flange, 273/318 used the flare/bell flange. 360 varied by application.