Not doubting you, but be sure the leak is not from another area... Get a flashlight, and check out the top of the engine (between carbs) around the thermostat... Coolant can and does flow quite a distance, especially when on the side stand.
I, and many others, have had a coolant leak 'up top', and had it look like it was dripping off the block.
Again, not doubting your initial check, just making sure ya look everywhere

Black Dog