question on these exhaust manifolds

My '68 Barracuda's 383 has a 1968 date code and HP designation. I found the manifold numbers identified in a reference chart below as:
383 1968-69 Barracuda& Dart / Right 2863900
383 1968-69 383 Magnum / Left 2843992

So what is this telling me about the manifolds? they are not a matched pair or what? Not clear what 'Magnum' means?
I have read that the 383 Magnum (starting in 1968) used the 440 Magnum heads, camshaft, and exhaust manifolds and the engine was advertised at 335 hp (250 kW; 340 PS).