If someone has the link to bleeching white tuffs,same thing.
Basically scrubb with scourer using jif or whatever its called now until clean.
Soak in bleech (not diluted)for week in large container. Just buy cheap bleech form Tesco 27p stuff as you will need a fair bit.
It take alot of patience,but it'll be worth it .
Sure someone does Z rim decals for rims.
Hope this helps