the reinforcements went on the outside of the body where the weld nuts were. it's not hard to do at all. cut/form the plate, drill the holes, and bolt it all together. done.
Plate steel? You can get that at any hardware store, in various thicknesses too - cut and drill to size, bolt underneath the sheetmetal (on the underside of the cab).
A Vice, a cheap harbor freight 4" angle grinder, and a cutting wheel.how does one cut sheet steel? Surely not with tin snips