Menubar Checkbox or Radio Button

This is not possible through the client events menubar script directly.
With some hacking at runtime, you could 'inject' your own JRadioButtonMenuItem or JCheckboxMenuItem.
Accessing the runtime client's menubar will be somewhat tricky; this post gets you some of the way there:

Actually creating the menu items you want to add is somewhat tricky; your best reference is probably the Jython manual: Chapter 16: GUI Applications — Definitive Guide to Jython latest documentation