Advice for LM/VM column build

[Will Stilltry]

Hi all
I am a total newbie looking to start work on my first still. After countless hours of research, I keep coming back to a plan of an LM/VM combo that was posted by Samohon in the first page of 'Diagrams and Plans' thread, allbeit some considerable time ago. (sorry, haven't worked out how to post a link to it!)
It shows a Boka slant plate LM head above a VM takeoff and gives some impressive figures for what it will produce.
The plan shows one centering ring below the VM takeoff and states that there are a total of five equally spaced rings down the length of the column.
What I am puzzled about is whether or not they are permanently fixed in place, and if so, how is the packing material inserted and removed?
I have also read many posts that suggest they are not required at all as the reflux will not run down the sides of the column and all they do is cause an unnecessary restriction for vapour to travel up the column. If this is the case, how come it appears to work so well?
I apologise if these seem like stupid questions but for the un-initiated any advice would be very much appreciated.

Will S