Turn zoom ring of the lens counterclockwise. The confusing thing with these later R16's is that you tend to want to grasp something close to the mount itself, but if you do that, it won't turn. If you turn the zoom ring (having first turned iris motor setting to "semi" and zoom motor to "stop"), it should come off fairly easily. Unless someone has really tightened the hell out of it. It's hard to get the hang of it the first time, but then it's easy.
Chambless lists two styles of Bolex eyecups as available. Their catalog is here: Chambless Cine Equipment Catalog You'll need to click on the link (on the menu that appears on the left-hand side of the page) for Misc. Camera Equipment since the individual pages of the equipment catalog aren't separately linked. The eyecups are listed down toward the bottom of the page that results.