Meehanite cast iron was used on all american made machine tools of good quality up until they were put out of business by the japanese and then china. The process of making meehanite cast iron is much more expensive and controlled then making other types of cast iron.
Unless it is specified if it does not say meehanite in the description of the machine then you can assume that the cast iron is inferior and a hit or miss on it's long term stability, and quality.
When machines were made here in the USA most companys had their own foundries and their castings were made at least a year or two in advance of being machined for finish purposes. It was also a good practice to rough machine a casting, let it sit for a while and then finish machine it later. This allowed the casting to stabilize also.
Castings were left outside in the elements in the north too as the temperature changes helped stabilize the casting.
Using a wood subfence on the warped fence is a good idea as the casting may not be worth machining if it was not designed with enough cross ribbing to help keep it straight and flat.
If you try to machine some bosses on the backside to help hold it during grinding it will cause movement issues,so good fixturing is needed .