Todd- the moly shaft is a win-win everytime...on my cars like the 67 camaro..i have custom mild steel drive shafts made 3.5 inches in diameter and 0.83 wall thickness and have had zero problems so far..
regardless i use Billet steel slip yokes..the drive shaft problems i have seen with my own eye's is the 1350 u joints and slip yoke breaking causing the drive shaft to fail....
Billet slip yoke all the way...cost is about $200.00 but well worth it..
Brian
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Bjuice..
"I'M YOUR HUCKLEBERRY ! "