In calculating the WACC, it's most appropriate to use:

the target structure because it's in some sense the best.

market values for structure and target values for costs because they're the most practical.

book values for structure and component costs because these reflect the actual existing capital structure and what the firm really pays for the capital it has.

market values for structure and component costs because the best reflect next year's capital costs which will be encountered when money is raised for future projects.