Here are the 2 suspects, based on what you posted.

1) Blown head gasket. You can do a quick (but not comprehensive) test, by checking for bubbles in the coolant tank. Smelling the exhaust at the tailpipe also works, for someone who knows what burning coolant smells like.

2) The water pump bolts were not torqued properly, the pump moved, and the timing jumped. If that's the case, you don't want to do the test described in #1 above, or run it at all, until the timing is checked. If Murphy was sleeping, and the timing only went off by a tooth or two, you might have gotten away with no valves being bent (yet).

So the first thing you need to do is pull the timing covers, and have your fingers and toes crossed that you will see the timing off by only one or two teeth.