This Truck is pretty heavy, and even in first gear, it takes some serious torque to move it. My first motor choice was the e-tek which is a PM motor, but after looking at the performance curves, it really would be pushing the e-tek to try and drive the truck.
Back in the 70's I got the bug to build an EV, and picked up a pretty beat 30V 400A 15 HP motor/generator from a surplus equipment company. This is a series wound motor that can take some serious power, so I decided I would use that instead. These motors have so much torque that the drive shaft can snap, so they use a torsion bar output shaft. The rear of the torsion shaft is driven by the rear female spline of the main motor shaft which is a tube.The output side of the motor has another external spline to drive the drive flange. The flange elongated slots engage the three raised post on the output end of the torsion shaft once the torque is high enough.A clever way to keep the output shaft from snapping under the high torque.
The drive spline will not be used on my coupling system so I cut it off with an air cut off wheel, since the shaft was too hard to cut with a bandsaw.