 Unlike earlier Mustangs, it was powered by an upright Briggs & Stratton 5.75 hp engine; this was coupled to the usual 3-speed Burman motorcycle transmission and a rear tyre with a tractor tread.These components were mounted in a new, specialized frame constructed of heavy duty 7/8" tubular steel.Originally available only with a rigid rear end, the Trail Machine gained a version with a swingarm rear suspension in 1964.