I worked with epoxy composites for six years with a good deal of time spent studying cure rates.
When an epoxy has hardened to the touch, it has only cured about 10%. A full cure can take years for epoxies that take a day to harden. Epoxies also continue to shrink with curing. Heat will hasten the cure with the cure rate doubling for every 10ºC increase in temperature. A higher temperature will also result in a harder and more heat resistant product. Epoxy also has a property called the glass transition point which is the temperature at which the cured epoxy changes from a rigid to a plastic solid. This temperature increases as the cure becomes more complete
If I were repairing the vise with an epoxy composite, I would fill the recesses generously and allow to cure at room temperature until hard. Then I would slowly increase the temperature until it reached between 110ºC and 130ºC. This process would take place over several days and the epoxy should be close to fully cured.
As to the composite, I would use a slow curing epoxy and mix in iron powder to make a thick paste. Not having the powder, saw dust from cutting iron with my horizontal band saw or filings from filing with a fine tooth file would work.
Fully cured epoxy is fairly immune to most solvents. I would expect good resistance to the chemicals that would be used in machining.