MM--"Countersinking creates a larger area of decay under and around the washer and nut."
The bark under the washer will die anyway. If the bark is trimmed away, new bark will grow around the hardwar faster.
I'm looking at the 2001 BMP's; what are you looking at?
MB--"I also plan on reducing the remaining limb as much as possible, but I don't want to leave a lion-tailed limb."
Butch, reduction is taking weight off near the end of a branch and liontailing is taking weight off near the origin. These are exactly Opposite. Please spend $15. to get the ANSI pruning standards so you understand what the *I&^*&^ is going on.
"Concerning sealing the crack, he wants to use that sprayfoam stuff. I said it wasn't necessary."
Don't dismiss it outright. I can see it possibly doing more good than harm, if it lessens flexing and doesn't inhibit callus growth. Also, if he gets to use the foam, might he give a little on the tightness?
"My main concern is this guy's idea about the TIGHTNESS."
Tom's use of the chart on page 13 of the BMP's answers that pretty well. If you spent $5 on the book you could point to it.
If you're committed to being bookless
you can use Tom's scary analogies "slam-dunk or karate effect" to carry the message.