80mm too short
Thanks for the tips, Jim! I definitely tried the 80mm bolt, making sure the pieces were lined up, no strippage, no extra space, etc.
It turns out the 80mm bolt sank 10mm into the threads inside the handlebar (the precious ten mils that I lost with the Kaoko).
I found a few close options at Fastenal, but not quite the match. Still checking all their nooks & crannies.
Mortons and Max were closed today. They're definitely on my list for tomorrow!