120 C, all though not great, should NOT be catastrophic and should NOT require a major overhaul again.
Alloy heads I'm assuming, it's possible you blew head gasket and water is in one of the pistons, don't panic. Pull the plugs, valve covers, etc as mentioned above, turn it by hand, clear things out. If water is in there
oil it up good and get it to crank over. I bet worse case scenario is pull the heads and replace the gaskets. The rings, rods, etc. should be still be fine. Might have warped a head, or two, resurface, re-install and get back in the ball game.