Further to my original posting
http://www.geekzone.co.nz/forums.asp?forumId=49&topicId=114791

Installing the master filter was a reasonably simple procedure. Just a matter of identifying all the wires involved. Then cutting into phone line wire and inserting filter using gelcap wire joiners.
I ended up with 4 spare line filters now. Tidys up the mess of wires around the phone jackpoints.
And below I have posted my modem stats from before and after. As noted by sbiddle I didn't get much of an improvement, but I'll take it.

Before


After