Прошерстил Гугл, нашел вот такие выпуск приблизительно 1927-28 г.г.
Но как на фото с надписью Бетут-Дамаск-Багдад не нашел.
Если в 1934 году компания Найрн пускала в рейс такие автобусы, этот факт никак не зафиксирован в той литературе, которой я пользовался при написании статьи. Странно.
Добавлено через 14 минут
Все, нашел недостающее звено:
By 1934, the Nairns were literally riding high - on new vehicles called Aerocars,
Buick coupes towing small coaches capable of carrying 10 passengers. They also
added a four-wheeled American Car Foundry coach - capable of carrying 24
passengers and fitted with reclining seats - as well as what was then the biggest bus
in the world: a Marmon-Harrington 38-seater powered by a l50-horsepower tractor
driven off three axles. This 21-meter-long vehicle (70-feet), purchased in 1933,
weighed 26 tons and gave passengers a smooth ride in seats modeled after those
used in passenger airplanes. Riders also enjoyed such amenities as a buffet, a toilet
and packed lunches.
Спасибо за подсказку, дописываю рассказ.