Hi Chris,
With the greatest of respect, the measurement of the Deffee ladder rung I think you meant it to read 34cm rather than 340 !! Well I took a look at the spreaders on my B36 from the cabin rooftop, and the photo attached show on my boat that the spreaders at their root are narrower than the dimension of the mast and would help to provide some clearance. Coupled with the arrangement of using sail sliders to secure the ladder to the track on the aft side of the mast, allows the rungs to stand away from the aft side of the mast and therefore provide a little more clearance. In the photo, the lazy jacks nearest the mast are about 40cm apart at the lower end and somewhat wider apart where they reach the upper spreader such that I'm pretty sure that the ladder rungs will easily pass the spreaders without any problem. As the maker of the ladders you refer to, and which I'd not heard of until your posting, they are located not far from where I live, so I'm considering going over to see the setup with a view to purchasing of one of their ladders. I'll let you know how it works out in due course.
P.S. From one now ex-biker to another, why are so many yachtsmen also bikers ?