6 N HCl has a concentration very close (but slightly above) to the azeotropic mixture water-HCl containing 20.2 % (w/w) of HCl and constant boiling point 108.6 C. Hence after boiling you will get 300 ml HCl of this concentration.
Aqua regia will decompose when heating, at least partially. So it is difficult to foresee an exact concentration of HCl. I can only safely state that last drops of distillate will show content of the azeotrope.