those are being re-popped and they are just B-body manifolds.
The passenger side one is correct for A and B but the driver side is a B-body unit.
If they are selling for 2k then I have a few pairs for sale. Last I checked B-body units like in the OP are going for 300. - 450.
The B-body manifold can be used in an A-body but the rear nut sleeves might have to be trimmed down a bit to clear the steering shaft on a RB and clearing the starter is going to be a little tricky ....if its a 4 speed then getting around the Z-bar is going to be really tricky.
A genuine A-body driver side manifold will resemble a C-body manifold and the dump Is not all the way to the back but has a longer dump tube.