Dave used crossover drive, like a tandem or most of Dave Krafft's bikes. This means the front cranks get swapped, leaving the pedal threads reversed. So he drilled and tapped new holes to get correct threading, and shorten the cranks to 155mm.
Seatpost from an upright bike does double duty. A section of tubing welded to the front supports the backrest, and the old seat clamp holds aluminum rods that support the fender.