That is pretty cool. I didn't know the 3.91 axle was called a drag pack. I took a 428CJ out of a 69 and put it in place of my 390 in a 67 and changed the gears from 3.50 to 3.91 and it was a real mover. The crane cam helped a little too. I did not like the 69 very much because it was hot...