Seized 289?

I was driving on the interstate in my 1970 ford mustang which has a 289 overbored 60 and when I hit about sixty-five, I had a major loss of power. I pulled over to the side of the road to let it cool off in case it had overheated even though my gauge didn't indicate it had. I have had issues with my cooling system including a still leaking radiator that I fill every time before I drive. I waited twenty minutes then drove it about three minutes to my house. When I got there, the starter went out and I replaced it. Then the engine would not turn. I tried turning it by hand and that didn't work. I took out the spark plugs and it still would not turn over. I then dropped the oil pan. It looks good under there as far as I can tell. What do I do now? Does the engine sound seized? How and why did this happen if it is seized? Also there was not water in the oil.

It does have an oil pressure gauge, but I don't know what it said. I didn't think to look. I drove it home about four days ago.

I did try the socket on the balance bolt. I got up under there and noticed that one of the sets of pistons on the crankshaft looked more dry than the others so I took the holders off it and the bearing was slung. Thank you for your help.