The pots on guitars such as the 335 are put in, and out via the wire routing hole from the trebel pickup, it's a very tight fit, and bloomin fiddly to get in and out.
To get them in, it's best to use the aformentioned string idea. When taking them out, you need to gently manouvere the pickups to, and as far into the hole as you can by pulling gently on the wire, and when you can actually get to them, pull them through the hole with some long needle nose pliers, or something similar.