"...can you link to or reference any authority to support the use of any poultice (charcoal or other..)for snake envenomation.."

I can not speak from experience about a snake bite (but I did come VERY close one time), however I can about a bite from another critter (don' know what). One day I received a bite from something on my forearm. In no time at all red lines started working their way uphill from the bite (as in toward my heart). I applied a poultice of cold water and baking soda, within about a hour the lines started to go back down, and within about four hours there was no evidence of a bite at all, other than a little red dot. Worked for me...