When I did my control arms I used straight apple cider vinegar, no salt or water.
But I wasn’t trying to submerge an engine block. That would take a lot of vinegar.
.
I'm using 4 gallons of apple vinegar, 1 pound of table salt and 40-45 gallons of water.
You can use white vinegar but it is half the strength of the apple vinegar. So you just use twice as much.