My '71 Javelin with a 304(215hp stock) w/ a 3spd manual tranny ran mid 15's and it was stock except the tires and air shocks. I ran dead even with an auto tranny Javelin SS/T w/ a 360(275hp stock?). We ran from a roll repeatedly, and were always locked dead even. I think the auto tranny and milder gear ratio ate up the extra HP he had.
I think 15's or low 16's is about right for his car. I'd be shocked if it ran a 14-anything. Of course, the best way to tell is just take it to the track!