The real problem is that the metal jamb is full of concrete. It is an interesting combination that eats saw blades. You will do best with a fiber blade that can be mounted in an undercut saw. There will be some minimal sparking, but mostly dust. It is possible to spray a light mist of water as you cut that eliminates both the dust and the sparks. The blades are relatively cheap, but they disappear fairly quickly - there is nothing to sharpen.
Weld cutting disks in an offset grinder work about as well, but are harder to control and won't stick out enough to make a single clean cut across the 2" of jamb. Carborundum grit blades for a Sawzall are SLOW and expensive, but will get the job done.
Steel cutting Carbide will work, but won't last long because of the concrete. A torch will not work. HSS blades will not work. Diamond will be destroyed, but will work.