good penetrating oil?

WD 40 isn't really for getting into rusted threads. Try deep creep or PB Blaster. There are others that should work for you. Usually the alternator bolts aren't that difficult,just a little tight and sometimes hard to get to. Tapping gently on the head of the bolt will help the oil to penetrate into the threads. I like to spray them and let them sit overnite if possible. I am unfamiliar with Rangers, so I don't know if you are dealing with a bolt that goes into the block, or maybe it has a nut on the other side. If they are nuts and bolts a lot of times I will just try to break them off and re-assemble with new fasteners.