A compression test won't tell you much about a head gaskets' condition unless there's something obvious, like compression coming from the radiator or a dead cylinder from blowing between two cylinders. A cylinder leakdown test would be better suited. Compressed air pumped into the cylinder (with valves closed) would show a smaller problem like a small gasket leak. Most people don't have access to tools like that but if you already checked it with that "block check" stuff, you probably aren't getting compression into your coolant. The condensation that's coming from your tailpipe, whether it's clear or black, is normal. If your headgasket was bad and was actually burning antifreeze, it would smoke only and would smell funny and be very obvious. If I were you, I would confirm that the headgasket was leaking extenally, put some GM pellets in it and drive it until the new engine was ready or something more obvious happens. Carry some extra antifreeze with you incase the gasket does go while away from home. Usually, when a headgasket goes bad, it's still able to be driven for a short while. When doing a compression test you can pinch off the fuel line with some needlenose vise grips to prevent flooding.
Good luck,
Scott
