Shot peening engine block question

[HawkX66]

For future rust issues... I've used the higher percentage acidity vinegar on quite a few things and it does better than Evaporust in my opinion. This gas tank was completely crusty and full of rust scale. It was a serious candidate for a new tank, but someone suggested the vinegar trick. I filled it, let it sit for a few days while giving it a good shake now and then. I did that three more times and this is how it came out. Not a spec of rust left. I've done it on several of my 69 parts and the results were just as amazing.