"expert old timer F/E - in-house - procedure".
First I declare my biassed preference to 3-crew ops with a real off-the-hangar-floor F/E .. albeit that 2-crew is great fun operating.
There would only be a problem if the AFM had a fuel usage requirement which was being subverted. If such didn't exist, then it is reasonable to presume that the fuel usage was not critical.
Re freighter conversions, and on the same sort of topic, when Ansett converted the Electras, they picked up an increase in MZFW by imposing a minimum fuel load in the outboard tanks for bending relief.
Love the WAI trick ..