Looking at the pin lying next to your ruler makes me wonder if this system of tightening/loosening, is something like an old lathe I have lying by me, If one looks in the horizontal holes in the headstock casting you will be able to see the transverse thro' hole in the pin, & the bottom of this transverse hole slightly up from the bottom face of horizontal holes.
take a portion of bar set up in a four jaw chuck & turn a slight length "off centre" thus making a cam shape, On the outer end of the bar cross drill for a tommy bar feed bar in, till cam portion is in transverse hole in the vertical tee bolt. Lightly push down or tap tommy bar in appropriate direction & this should take the pressure of your tee bolt section & allow head or tailstock to slide free