You'll be well out of 3rd gear before the end of the track with the 4.10. I wouldn't want to run that much torque through the 518 OD unit. Not to mention they are not real effecient.

3.55 Dana would be your best option with the good Trans parts in a 727.

3.55 gears are all over the place. If you're on a budget get a used one and swap it in. That's what mine has in it.