The old Flxibles had 6-71 series Detroit Diesels in them for the most part. The 6V92 didn't come along until the 70s. If this one is an old Prevost it looks remarkably like the old Flxibles...Cool stuff for me. I drove for Greyhound for a few years in the 70s and actually drove the Super Scenicruisers (GMC PD4501 model) double deckers on routes with passengers and freight (built from 1953-1956) . They were powered originally by two 4-71 Detroit Diesels and a 4 speed trans with a two speed axle. The twin didn't work. They re-powered them with 8V71s and locked the two speeds in high range. They were tough then!!! The driver write-up books that always accompanied each bus had a gold star on the front of them denoting a million miles travelled and most of these old gals had 6 gold stars!!!!