The Dana is not overboard. I did it first with my 318, and it is perfect with my 408. I have a line on a guy who sells them reasonably. Maybe he'll give a discount if I refer you to him. I paid $1850 for mine new with 4.10 gears and disc brake conversion with drilled / slotted rotors. It was all set with spring perches and bolted right in. The 904 would be fine. Crate 408 usually are in the high 300 to low 400 horsepower. I don't like crate motors because you can do so much more with a 408. The biggest 904 issue will be the 1:1 final, so give some thought into where, how much and how you will drive and choose your rear gears carefully. I have 4.10 and it was very hard to drive on the highway at such high rpm. I almost went to 3.55 before I went to an overdrive.
