Essentially, you remove the step pulley at the rear of the spindle, and then the dust cover and bearing preload adjuster at the rear (behind the pulley. Then remove the spindle by pulling it out from the front. Don’t drop the tapered roller bearings. (You will also have to remove the six bolts that hold the t slot face around the spindle at the front, which it appears you have already done)
My particular step pulley was attached to the spindle via a tapered flange bushing. Removing the sliding head itself is a bit more complex than just removing the spindle, as you will also have to remove at least one outer spindle bearing race and the sleeve that goes around the spindle that the head lever and motor arm turn on.
