Phew!
Found the scans. Looking closely at the pic below, it's not immediately obvious if the tail-plane is white - but having seen the original slide projected onto a large screen, in the original 'Kodachrome' hues, it is white, as are the other aircraft photographed at Prestwick on that day. The top of the fin extension is certainly bare metal in these pics, and also in some others I've filed from the 'net, and in my 'Canadian' book.
But !
All of these are in the period of the old Red Ensign flag, still in RCAF days, and all around the same period, which leads me to think that the 'white cap' to the fin is date related.
One thing I hadn't picked up on, until you mentioned it Andy, was the grey surround to the auxiliary intake doors, which is also on '771' in the pic below, so thanks for that - I'll add the outlines to my model.