FWIW I still have the stock shafts in the 727 in my cuda. It's over 3800 lbs and ran mid 9s NA from 2006-2015 w/ no trouble. Been running 8s on nitrous ever since. I don't race it very often though.
From what others have experienced, it wouldn't surprise me if it snapped something the next time I ran it. twocents

CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax