[Cglrcng]

Have seen many (youtube videos), of people doing plastic drum anode electrolysis on rusted blocks and other cast iron parts/pcs. (You would need/ o watch a few vids to get the chemical and electrical choices that they use, but I have seen amazing results (the water and chemicals they use may be a hazardous materials issue later as the drum is usually pretty mucked up once the process is completed). Have seen them use Welding machines to battery chargers for the DC current as it flat boils the rust away.

Then maybe an immediate hot tanking and bead blasting & then full machining at a machine shop), as soon as it is
removed from the drum. Torch all exterior surfaces w/ Propane or Map gas torch to remove (quickly cook away all grease and oil on exterior surfaces after that, mask and paint ASAP after short block assembly). Personally I like Dupli-Color Engine or Caliper Enamel with ceramic as it withstands up to 500 degree temps and oil and other fluids, resists chipping due to the added
ceramic.

Have seen some pretty rusted cast iron blocks, pans (as in cookware), look like new once done. Just make sure you do it outside in open air as it creates an acid during the process.