"Pison" is dialect for "poison"--and poison here meaning pretty much "very."
In a colloquial sense... you could almost say "damn" instead, and I think
Twain might have been aiming for something strong like that.

I suspect three-day draft means a bank draft that is post-dated for three
days later, which is obviously  a scam.  But maybe somebody else has a more
definitive answer.

Hope that helps, and good luck with the translation!

John Bird
Winthrop University