.120" is to thin for a cylinder wall alone zorg asuming when you bore it out you remove all of the cylinder. If you do that you might also have an issue with fitment as most "sleves" are ment for a full interference fit where as a liner is ment to stand on it's own... sounds like your trying to make a liner out of a sleve... also at that thin of a wall you will have heat transfer issues which is what is causing the cracking... .140" is the minimum rule of thumb wall clearance.. Why not get a thicker sleve.. you should be able to find one for that size bore.. if you only have .240 between each hole after the sleve you have a whole nother issue with heat transfer as two sleves can't touch each other. If you give me the bore dia I can find one as I do sleveing on engine blocks all the time.. no since making ur own sleve when just a thicker cast iron sleve will do...
