I certainly do not want to discourage anyone from pursuing all possible avenues to find their ancestor's records. But I would not get my hopes up about finding anything in the archives. By treaty, when the AH empire was broken up after WWI, the archives were suppose to turn over all records after 1867 to the successor countries. Unfortunately, the ones turned over to Slovakia have been destroyed. Unless your ancestor was an officer, neither the Austrian or Hungarian archives will have anything either. This is a very frustrating fact for those of us descended from Slovak soldiers. But perhaps the archives will be able to help you identify the uniform.