I've been consistently running 17.50's for the last year with my nearly stock 250 I6 in the 1/4 mile. I just swapped on a modified log head with a 350 Holley 2V, directly mounted to the log manifold. See details on the head with pics on my post in the technical section. I was hoping to maybe get into the high 16's, but was quite surprised when my first run with the new setup was a 16.52! The bottom end of this motor is completely stock. My best run on the day was a 16.35 at 81.77 mph. I ended up taking a first place in my class with the new setup!
Yes, an aluminum head is in my future...probably when I do a full rebuild with all the goodies. In fact, the head I just swapped on was re-worked by classicinlines.