We have now made contact again because I was having a week in Majorca dodging the thousands of cyclist's there! I missed this thread.
I only use Mintex discs now because with lesser makes they are not always parallel because my conversion mounts on the opposite side to standard VW GTI Mk 2 239mm discs.
Brakes can stand non concentricity but not side play run out. Though single pot calipers are very tolerant of some side play unlike the standard Triumph setup. I have just done a set up for a rally Sprint as he broke a standard caliper's lugs off possibly due to stub axle flex!
I will be here for anyone who needs any info as no more holidays are planned yet.
To answer the original question the bore needs boring out to 66.7mm and the holes drilled to match the Triumph hub, these will then bolt straight onto a standard unmodified hub and the clamp ring that either can be a cut up standard disc or an alloy ring which I make and standard 3/8 UNC bolts are then used. I hope this helps.