I was unhappy with my office chair, so I engaged in what became a two-stage conversion.
Step 1: increase leg-spread room, and create space to play my guitar without having to lean too far forward to avoid chair-arm. This was achieved by sawing away all of the chair arm except the L-Bracket which attaches the seat to the back.
Later, I decided I wanted it to be able to recline without tilting the seat. I un-anchored the top rear bolt from the arm, pushed the back waaay back so the hole would be proud, and re-affixed the bolt. The chair-back with that bolt was now free to swing back and forth, secured, as it was only by the lower rear bolt. I did the same mod on the other arm, happy to sacrifice elbow rests altogether.
I loosened the bolts to the seat. I was now able to wind stout nylon cord three times around the forward seat bolt and the upper back-bolt. Adjusting the angle was then a simple matter of untying the knot, tightening or loosening the 'pulleys' on either side, then re-knotting.