As has been said, just remove the corroded heat shields, but only if they are badly corroded.
Exhausts tend to rust, so general cosmetic rust does not affect its performance.
Aftermarket exhaust, including Y section, is the way to go when the time comes.
I am dismantling a 370 early next week, so parts will soon be available, but reading your post, it appears that replacing these parts may be unnecessary.
Alex.