72' 340 Drivers side HP manifold vs older HP manifold

I have a chance to buy a 72 casting number LH hp exhaust manifold and a 70 RH HP exhaust manifold,

Question. Is there a performance difference of the LH 72 manifold versus and older casting number LH manifold, say 69 or 70?

Also, What are they worth$$ ??

I have headers now and am also wondering if there is a significant difference of performance between the headers and the the two hp manifolds in question. My motor is a mild built 340.

The LH manifold casting number is 3614368-1. Dated 3.27.72
The RH manifold casting number is 2863549 no date maybe there is a L2 also cast into it.

Thank you so much!!