The carb price maybe about right, but he is really high on the Offy Intake.
If that is all want I would think 500.00 would be a fair offer.
Concerning the engine, a lot depends upon what was done.
Was the head redone with new seats and guides? When the cam was changed, was a new timing chain installed, was the cam degreed in or just set up dot to dot. That looks to be a hydraulic valve cover, is the new cam mechanical or hydraulic? I see the .030 over pistons, new main and rod bearings?
Does the seller have a receipt listing what was done, if so and it checks out with what was done 1000.00 is a good deal. If he does not have a receipt, the seller should at least know where the work was done, so then contact the machine shop to verify what was done.
If the seller can’t verify even that then I would consider it a core engine and you are really just buying the intake and carb for 500.00 and 75.00 for the core engine.
So with no documentation 575.00 tops is a decent deal.