Model: "Mighty" style. It's difficult to tell the exact model due to it being a left hand crank. The date code of 47-8 means it is likely from August 1972, according to http://www.vintage-trek.com/component_dates.htm#sugino.
Length: 175mm
BCD: N/A (Left crank arm only)
Date: 47-8
Pedal thread: 9/16" x 20 (standard)
Weight: appx 169g
Other info: In very good condition overall. Some marks (see pictures)