in too deep: trying to go BBP on a 68 barracuda and its going.. poorly.

Emailed Cass at Dr Diff and asked about these axles. Axle Pkg Stock Length Mopar 5X4 1/2" Bolt Pattern (pair) $298.00 Doctor Diff high-strength, 30 or 35 spline axle package. Question, are theses axles sufficient for 500+ HP?
His responce was, "I don't recommend ANY 30 spline axle for 500 hp if you drive the car hard, especially with a manual transmission. That is why NO manufacturer will warranty a 30 spline axle against twisting/breakage (Mark Williams, Strange, Moser, Currie etc...). 35 spline axles with a spool are fine, though."
Does any one have any experience with this product? I have read, even on thos forum that a stock 8.75 rear end could handle 500HP. and these are high strength axles. What are your opinons.