How much to Shorten a Rear Axle Housing?

How strong will resplined rear axles be? Enough to handle approx 500hp? Is there any offset for a 70 dart swinger. I am moving in the springs to the frame rails so I am looking at shortening the rearend. I don't want to be limited to an A body 83/4 as they are getting hard to find. I may need the abody axles though as I have the small bolt pattern. Any thoughts on this guys? :newb: