Welding cast iron can be very problematic and is not suitable for any kind of stick or arc welding (with the one exception of malleable cast iron). Brazing or welding using an oxy-acetylene torch is the usual method, but the entire working area has to be brought up to temperature to avoid the chances of cracks appearing. If the unit is plate steel then arc welding would be easy to do and virtually fool-proof. You could check if the metal is weldable using arc welding by a quick tap with the rod in an unobtrusive place - if the result is a mini 'crater' then it is unsuitable. I once repaired a lug on the travelling carriage of my Dominion Industrial Radial arm saw (about 25 pounds of cast iron) with araldite epoxy. 15 years later and the repair is still going strong! Hope this helps.