Forgot a couple of things.
How to get the post number: hover over the reply or single-quote button and either 1) read it from the url displayed at the bottom of the browser window, or 2) right-click and select “copy shortcut”, then paste the url somewhere and extract the post number.
The “post=” code became available with the version of vB we now have. More info via the vB FAQ link at the bottom of the page.