You should not be looking to replace any of those components to be honest… In your picture they look absolutely normal. What is it you hope to gain by replacing the backing plate?
If your drums are warped they will cause the shoes to make noise as the drum is no longer concentric internally and it will be tweaking the shoes and springs and everything inside the drum…which will make noise. The shoes are meant to rub just slightly on the drum when they are adjusted properly…if the drum is no longer perfectly circular inside…it will move the brake components and make a creaking/knocking sort of sound.
If I were you I would leave the backing plate well enough alone…and focus on maybe some new shoes and new drums. In the process of new shoes you will also clean up the dirt n dust back there as well.
With new drums and new shoes… I bet your sound goes away. In fact I have 20 bucks sez it does.