If you only blew out a quart and a half of coolant probably all is well. Of course the engine was hotter than usual but not hot enough to boil most of the coolant out. Could the swish noise be related to the new belt?
It is always important to keep the gauges properly functional. You may still not catch a condition in time even with them working. If not working generally you will not catch something till too late. You were lucky this time in my opinion. Also I wonder how many of our members ocassionally inspect the condition of the rubbber belts for cracking and wear etc. Always cheaper to catch them early.