it appears that the tutorial in the link is rather complete.
the best thing too do is to make the circuit, run the motor and make sure that your motor is capable of moving the threaded rod and that the drive train can move your 68 inch dobsonian !
the first part of the match is distance from the axis to the screw will create the triagle. trigonometry will reveal the distance the threaded rod has to move to change the angle.
your motor, the setting on the EasyDriver (which should work fine) and your pulse rate all come together to move the axis at some rate. all that is explained on the second page of the link.
part 3 offers some of the authors settings
static const float STEP_SIZE_DEG = 1.8;
static const float MICRO_STEPS = 8;
static const float THREADS_PER_CM = 8;
static const float BASE_LEN_CM = 30.5;
notice how this is in a little box ? this is done by using the # above, it gives a place to put any program code and is the preferred way to post ANY code when posting on here. please note that for future references to posting code.
the bottom line is that once you have made the unit and have tried it out, you will need to adjust the code to make it move your modified version of the threaded rod.
as you know the barn door tracker is flawed in that it only works for a short time before the movement of the device departs from the rotation of the earth. this does offer short periods of good enough alignment for photography or viewing.
I would offer that once you built it and tried out the movement, come back and ask for more help.
I see that a home or end switch should be installed and I would add a pot to alter the speed on the fly as well as a readout to show some of the parameters. since your device departs from the one in the link, the sidereal time will be different. the link allows for the ever changing angular movement vs the earths rotation and allows for a few hours of operation.
in my view the best path is to follow what the link offers as close as you can. once you get it running, the issues of movement will become clear.
in the simple review of your parts, you are on the right track and your parts should work.