The set up is fine, so long as (1) the tarp doesn't leak and (2) the level of the mixture is above the items being soaked. Special care must be taken to rotate items that are not totally submerged, or you may get a hard-to-remove line in the item where the level of the solution was.
Remove the fender braces if there is plating on them still. The acid will gradually remove the cad grey plating.
Wash out dirt and work out the dents on the fenders before soaking.
De-grease all parts before soaking.
You'll have a fair bit of bare metal on the insides of those fenders once the soak is done. The outsides actually look fairly good, so you may not see much improvement there.
Check the bath every 20 or 30 minutes if you are unsure of how things are going.
Staining from oxalic acid soak usually is a symptom of either too strong a mix, or too long a soak. The staining usually is a dull yellow color. Sometimes it can be removed with a little effort, but sometimes it's tougher.
Do not allow to soak overnight. Do not soak any pot metal parts.