I hadn't been on Robert Carrolls Yahoo site for a while so went for a look this morning, his list of data has expanded and there is now a 1968-69 working book and the Glasgow to Colchester is still there! The Core formation was now 1 x BG, 1 x SK and 1 x CK with an additional SK on Fridays Only. Additional vans (3 x BG and 2 x GUV) from Colchester, Liverpool St, Biggleswade, Spalding and Yarmouth which were detached at Edinburgh for Glasgow Parcels Station (Salkeld Street). Interestingly the train now was used to convey the Kings X to Fort William overnight Sleeping/Day cars (BSK/SLF/SLSTP and BCK) from Edinburgh to Queen Street (MSX) which were detached from the Aberdeen sleeper at Waverley and were then attached to the 06:00 to Fort William (see my post above) so the train must have arrived at Glasgow around 05:30.
Edit Further reading shows that the train did not appear on the Carraige working booklet from 1971 - 1972, so this service met its end in May 1971, in its last year it ran under the headcode 1S38 (down) 1E50 (up)
JIm