The performance capability difference between approach (OEI) and landing (AEO) climb cases wasn't well understood at the time and Joe - nice guy, I thought, although I never flew with him - was the unlucky fellow whom it caught out.
Indeed, the ICAO PAMC on performance was in the process of being adopted in the mid-60s and, up until then, performance certification was a bit hit and miss, being based on older piston designs.
Had Joe experienced his situation a few years later he would have not been caught out due to the added protection mandated by the newer procedural protocols. As I recall John Walshe - a charming gentleman's gentleman - was the performance boss at AN around that time and he was nobody's fool when it came to performance engineering work.
Since the performance rules moved to the PAMC requirements the certification basis for all heavies has the approach climb WAT for OEI gear up and the landing climb WAT for AEO gear down.
It is for this reason that the standard missed approach sequence from the normal landing case is thrust/flaps/gear to cover the OEI possibility. Also, if one fails in the landing configuration and the aircraft is not on very short final it probably makes a smart move to reconfigure to suit the OEI situation.
Likewise one should run with approach flap for an OEI landing or else accept that a low level miss is not on the gameplan if land flap is selected late in the approach.
In Joe's case, the higher drag put the aircraft in a parlous situation to start with after the engine was secured. The trap was that the situation is masked during descent due to the lower thrust requirement but becomes all to clear too quickly when one endeavours to level off.