You likely already know this but do realize that old paints and fillers, on old machine tools have a very high probability for lead. So you will not want to have young people around when refinishing the paint. Clean up is important too.
Unfortunately machine tools are a tough environment for paints. If you want better life than what a rattle can from the local hardware store can offer you will need to be willing to spend on pro quality paints suitable for machine tools. In that regard you have two basic choices, Urethane and Epoxies. The rational thing to do is to visit some local paint supply stores and get a handle on what they offer.
One example of a high performance "paint" is "Imron" from Dupont used in the transportation industry. Now that is a highly specialized coating system that probably isn't amendable to DIY usage. Rustoleum sells an Epoxy Mastic paint to the industry that is probably better suited to DIY. Try this page:
https://www.rustoleum.com/pages/industrial/resources/product-specs/. Generally what you will run into is the better the coating the more difficult to apply. Imron is slightly notorious in this regard requiring special equipment.