oil in my water???

My 91 Exploder got a little hot (not to the red ) I stopped to add some premixed Anti-freeze and added it without shutting the engine off. I've done this before and I think it's supposed to allow removal of the cap easier on a hot radiator. The cap came off with some steam but not too bad, I added the coolant and just before the radiator got full I heard the RPM drop and a miss developed. I had another 10 miles to get home so I limped back with steam blowing from the tail pipe. I know I have either blown a head gasket, cracked a head, or cracked the block. I have oil in my water but no water in my oil. Does this indicate my head is cracked or blown a gasket since there's no water in the oil?? I have 210K on the truck and have replaced the rear, manual tranny and the engine over the past 14 years. If it's the block, I'm driving to junk yard. If it's a head, hoefully the left, then I might go ahead and do it. Any thoughts out there, I'd be glad to hear them.