Cast iron cleaning and filler

I have a cast iron bell needing a thorough cleaning and a few pocks that need filled.
first question is what is the best way to clean?
I have seen sulfuric + phosphoric bath methods.
Question two, what is the reccomended putty filler to fill small pockets (only about 1/8" dia + 1/8" deep)?
I have come across the devcon 'plastic steel A" being reccommended. However, I have also been told it is better to use an epoxy with iron to achieve a filler that expands/contracts the same as the base metal.
would these be the same? is the steel putty just filled with iron?
ANY help would be apprreciated. even if it isn't an answer to any of these questions.
Thanks so much.

You can use 5% ammonium citrate solution(mixture of 50 gm citric acid/1 lit water and add some ammonia,pH must be 3,5- citric acid without ammonia works too ).As filler you can use mixture of iron dust and some epoxy glue.Good luck and hope it helps!