1. Yes an engine can be too cold
2. Even with no thermostat, this engine is not going to be damaged as long as it still reaches normal operating temp...190 I think (see rave)
3. I'm in Texas and running an inline mod with a 180 thermo in it.
If you live where it snows, you will probably want...
The heads look like heads...just dirty valves thats to be expected on these.
If you are re-using, make sure to take those to a machine shop and have them checked/repaired. I use Precision Engine in NE Austin