In each case (photo), to increase seat travel you must grind flush the pressed-nipple *or* flat-rivet (as the case may be) which is closest the "no-paint-path" which a roller-wheel (not visible in photo) has worn via friction. These two obstructions must be ground-smooth in unison as they are contacted by roller-wheels at nearly the same instant. This will give you about an extra 1/2" of seat travel. This may not sound like much, but it will surprise you if you've truly been wanting for space.
It is possible on both tracks to grind off the following flat-rivet as well, but that will require that you weld the brackets together on the back-side first, as too much structural integrity would be lost otherwise. I have not done this (second) step, but it should result in the seat-back contacting the rear bulkhead, beyond which any further travel would be dearly won.
