head gasket on a KA isn't fun...takes about 4 hours for me...probably 2x that if its your first time. There is a tool you can buy to check for hydrocarbons in the coolant that will tell you if there's a headgasket out. otherwise check the usual signs...oil in coolant, or coolant in oil. oil will look milky and lighter than normal. check those signs i mentioned above, before you try a headgasket.