here is a cb350 piston (top- .25 over actually, but the other dimensions are identical to a STD piston... the one i have just has a big hole in the crown), next to a yosh 811 piston (bottom).
measuring from the bottom of the pin, the distance to the 811 crown is almost the same as the distance to the bottom of the cb350 crown, meaning you'd literally take the entire crown out trying to get down to the dimensions of the yosh piston. there is definitely not enough meat in this one to have 10.5/1 CR. like i said, maybe there was a particular year with thicker crowns?