start off with liquid wrench, spray it on liberally, allow to soak and then wipe. After that it is liquid wrench as the medium and wet/dry sand paper starting at a rough grit and working towards fine. I have refinished one other cast iron top such as this for my grand father in law. Get her nice and shiny than coat with a good carnuba wax to prevent future oxidation.

I need to do this on the work surface for my new to me drill press as well.

I am thinking about stripping the angle irons for the bisei and having a buddy powder coat them to avoid any future issue. The rail tube its self I will strip and paint. I don't want to add any extra width/height to the precision piece and I am afraid that PC by it's nature will be too thick to use.