Will a Stock 489 handle 700hp?

Slicks can spin a little at the strip, and still recover and post a decent time. Drag radials only work well as a dead hook. If they spin, the only way they recover is to completely chop power ( also, NOT good in first gear for your 727), therefor drag radials are HARDER on the drivetrain than slicks!
The $1200 dana above was built from a truck dana that probably had thicker axle tubes and floater axles. So, it was narrowed, had new axle ends installed, new custom axles, and an unknown gear and suregrip, or spool, installed. Thats how to save half the cost of a new strange (dr diff) 60.
Just about any guts in a 60 will live forever behind a small block. I personally would choose a 35 spline clutch suregrip. They have gone billions of miles in trucks. I dont trust the gear style, i have heard too many complaints.