Incredibly detailed build log, and major props to you for making the plans available.
I'm also impressed you addressed the pallet safety issue, which was going to be my initial question. I'm not 100% sure it's safe, based on your post, but you're absolutely forthcoming with the fact that it's not a definitive test and you approached it with a good level of rigor.
Heres a good cheat sheet for you:
The treatment code : [HT] = Heat treatment / [DB] = Debarked / [KD] = Kiln Dried.
If it has any of these markings, no toxic materials were used in the construction of the pallet. This doesnt guarantee there couldnt be spills after the fact which was the point of the pallet safety post.
I was unaware of the treatment codes, that's useful.
My main concern was the spills - I've seen enough stuff spilled in my lab that I'm a little wary. Still, you did a pretty good analysis in that post and the 100% sure thing is just me being nitpicky.