You do what you do on the extraordinarily rare occasion it happens OCTA: overtake, in accordance with the rules of the air.
Except that it wasn't OCTA, it was in CTA, so under the system of the day, the clearance was only available at a different level. At the time, there was no emergency situation, it was just a routine request for a transiting clearance, and treated as one, so WM ATC could not offer a faster aircraft the same track at the same level as a just cleared slower one.
Rules of the time, maybe different now, but that's how they were applied. OCTA and CTA were two very different things, with very different service provision and requirements, unlike the alphabet of today.