Hi Owen,
That all sounds correct to me. What kind of Stepper driver you you have and what are the input specifications?
You might try a max width pulse with:
FPGA(STEP_PULSE_LENGTH_ADD)=63 + 0x40;
and inverted with:
FPGA(STEP_PULSE_LENGTH_ADD)=63 + 0x80 + 0x40;
Regards