hellbents measure about 5 cm longer than they are but they ski insanely short
if you think about it there's very little ski touching the snow because of the rocker making them feel very short. you'd be fine on either the 169 or 179, if you're gonna mount center go with the 179 but if you're gonna mount recommended maybe go with 169
for reference look in my pics, the 179 bents are technically the shortest skis in my quiver but they're longer than my 185 jj's