steam erupting from tailpipe

1989 f250, 460, The truck has been sitting for about 4 months, runs pretty well. 89,000 miles. Has a cooling system leak, not sure where it is going but not into the cab or onto the ground. Started it this morning and a huge amount of steam boiled out of the tailpipe and it continued for about 5 mins until I shut it off. Lots of water dripping from the tailpipe. I think that there is a very obvious answer but I am not mechanic enough to come to a firm decision. Thoughts?

Check if mixing with your oil.

No bubbles/froth. Color is uniform, no light brown hue on dipstick above the oil line. Oil level does not go down so maybe there is water. Would it be helpful to put a load on the engine and then check again? Maybe the water would burn off. Assuming that the water would do no damage of course.

Ok, my 98 it is the lower intake gasket has gone bad and is leaking coolant into the intake and then flowing into the combustion chamber. But it is a V6. I don't remember the top of a 460, haven't seen one apart in over 30 years. But for that engine I would from what I remember going out on them, think it was a cracked head or block, not a intake gasket problem. But you could be lucky and it is a head gasket gone bad and the leak coming from there. A compression test of the cylinders and coolant system pressure tests would be the first things I'd try. But most likely the heads are going to have to at least come off. Just hope it isn't the block cracked, as that would be your worst case scenario.

Thank you all for your help. The truck, with all of its many warts, is going away.