Lets deal with the car first; a direct fuel-injected straight-8 engine, 310 horsepower, and a top speed of 180 mph. Pretty quick by today's standards but back in 1955 (60 years ago!) this was as good as it got.
Moss, along with co-driver Denis Jenkinson raced it in that year's Mille Miglia, a 992 mile circuit taking in the Italian countryside and narrow streets of the towns in between. They won it too, with a time of 10 hours, 7 minutes and 48 seconds.
Way behind in second place and in an identical car was Juan Manuel Fangio, already a two-time Grand Prix World Champion by that point. So when Moss describes the race as the greatest win of his career in this film, you're inclined to believe him.