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 inside driving. Had to use the air all the time because the roof vents were removed in 69 and up. Loved my 67 and it is the only car I wish I had back. I have another 67 but it has a 427 small block stroker. It is faster but does not sound as authoritive. Has my 3.91 gear set in it.