I agree with most of what ahy says. The only exception that I would take is that he feels that an 8 3/4 would be "marginal" with a 408. I run a 489 8 3/4 in my Cuda. 3,500lbs, 500" stroker, 4000 stall, 3.91s, and drag radials. The car will pull low 1.5s 60 foot. I get years out of my gears before they get noisy.

A 60 is pretty much bullet-proof, but an 8 3/4 would be cheaper, easier to set up, easier to find, lighter and eat a few less ponies while lasting a very long time. And is much easier to change gears in should you want to try a different ratio.

Also, if I am not mistaken, I believe that many Dakotas came with an 8 1/4 with 3.55s and a Sure-Grip. And the junk yards (pick-a-parts) have a lot of them now. $50 will buy the gears and carrier at most places if you pull them your self.

Good luck with what ever you decide.