Re: O Sensei bokken
I have never heard of a koryu that didn't treat practice with a bokken as a safer substitute for practice with a shinken--i.e. you treat it as a shinken in every way, including drawing, using the edge to slice not strike, not putting your hand on the edge, and not using the edge to block. Absent evidence to the contrary, I would assume O-Sensei had the same attitude. My experience with koryu is very limited tho, so I'm open to correction.
The story I heard about Iwama bokken is that they asked O-Sensei one day about a sword technique and he picked up a handy ax handle to demonstrate. So they made their bokken like ax handles.
Probably a legend, but too good to check.