Early Sure-Grip Questions

I just found out the hard way that I have an early model sure grip with the 2-piece splines and my axles must be too short. I was driving it and decided to get into it a little bit and bang. Car felt like it was in neutral and would barely move. First thought it was my tranny. Limped it home and started investigating. After removing axles and center section, I discovered about 3/16" of the end of one of my axle splines are gone. I guess the axle wasn't engaging the inner splined section in the diff enough and it let go. What's the concensus on these early type sure-grips? Are they any good? What kind of power can they handle if used with the correct length axles? I'm running a 416 that is probably putting around 400hp or maybe a little more to the wheels. I see that Mancini has Yukon axles in the longer length for the early type sure-grip. I am running Yukon's now, but they are about 1/4" shorter than the factory axles. Are the Yukon's strong enough for my application or should I look elsewhere? Thanks.