Finally got to installing the wiring harness on my 12 string 335 today, and let me tell you it was a mammoth effort. Anyone who has tried to do this will tell you that it's a bugger of a job to get a set of connected pots through the F-hole and into place with anything less than a childish tantrum or two.
In the end I sucessfully used the "fish-tank 5mm pipe" method to complete the task. This involves threading pipe through the holes and onto the tops of the pots (and output jack) and then drawing them carefully through the body until they are seated and can be affixed. It takes alot of fiddling as the wires can easily become tangled or trapped between pots and the guitar body, and the pipe can be easily detached from the pots, but finally after 5 attepts and re-starts the components were seated and finger-tightened - job done!
All that was left to do was to add the glorious gold top-hat knobs from Stewmac and then it was off to the ball Cinderella.