From my readings most native users as well as western users of Ayahuasca brew with the entire vine, not just the bark.

Lol, I think that number is EXTREMELY low.  I have read that the LD50 for IV'd DMT is around 10 grams for a 250lb male.  Reasearch that has been done on full stregnth Aya brews show that by the time one ODs on Aya they are extremely close to ODing on the water in the aya.  It's that safe.

I posted the paper I got this from somewhere on this site...if I have time I'll dig it up.  8mg/kg just seems so increadably low for oral administration. 

He makes some extremely conservative (and wrong) assumptions.  112mg is just not right.  I've known people to smoke 250mgs+ DMT in a sitting (not often, but I've seen it before).  Even at 1/2 potency that's 125mgs IV dosage.  I think he puts the risk of DMT way too high.  Many of us would be dead if his assumptions are correct.

5-MeO-DMT has a much different safety profile than DMT.  5-MEO-DMT is usually not considered to be safe to take along side an MAOI.