Merckx did use the earlier style of bb shell with brazed on straps, but, as you say this is a different, later, time period. You can see in the marked up image vestiges of the cast in grooves that remain after the wings / ribs you see in the picture of my unmodified bb shell are ground off. As a side note, some Merckx frames used the Vitus bb guide for a short period. I believe most of the reason for changing to under bb cabling have been just cost saving. A small cost saving per frame adds up over a year's production. Thanks
sthurman for the brake bridge picture, that's the unmodified Silva bridge, some around that era had a lightweight version of that bridge.
