Variable speed control of a DC motor
It's a 3-phase motor, hence L1, L2, L3. Also, more directly, PH: 3
You will need a VFD for that. Your KB controller is for a brushed DC motor.
The good news is that the VFD + 3-phase motor will probably give you much nicer control for your lathe than a DC motor would, including low-end torque for turning larger diameters. Leeson is a good brand of motor.
A VFD (Variable Frequency Drive) in this size range will typically accept 240VAC single phase input and output 3-phase at varying frequency to change the motor speed. Some accept only 3-phase input and some will accept either, but operate with a derated output power when fed with single phase, so take care in the selection.