Where to start with a rusty block?

if the block is oily get some pure white tide . put 1 cup per 3 gallons of water in a tub from home depot and soak it for a day.

rinse well

buy oxalic acid crystals online . mix them 1lb to 1 gallon of water .

fill the tub and soak the block for 3 days.

do not breathe the fumes ad do it in a well ventilated area.

your block will look new.