[Cool Hand Lurker]

I would leave the petcock open with an empty bucket underneath and get some heat blowing on the engine for a couple of days. Wait until the water comes out. It takes a long time for ice to melt when it is enclosed and depending on heat coming through a cast iron block that is "just above freezing".
Don't pour water into it until you are sure it is thawed out and emptied out. That water could quickly freeze up around the existing ice and create more problems.

Many lessons are learned in Minnesota winters !