I don't have a Lang but I do have a reverse flow made out of a 120 gallon tank so it's a little smaller than a Lang 60. With that being said, I did a hog a while back and this was my wood/charcoal consumption for a 12 hour cook:
2 - Weber chimney's full of Kingsford Blue
14 - splits of seasoned wood approximately 16in long by 4.5 inches in diameter.
I ran it at 250-275 the entire run. After getting it up to temp with the charcoal and 3 pieces of wood, I was only using one split every ~75 minutes.
120 gallon reverse flow aka Hog Coffin, 18.5 WSM and starting SpatulaMan BBQ in 2013