The additional strength that the 9 inch Ford gained part of its reputation from is the fact it uses a 3rd smaller bearing at the tail end of the pinion gear. What kind of engine and torque number do you expect to be running? With limited available traction on the salt I'd think the tires would be the safety valve that will prevent the rear axle from taking severe abuse. If the tires can't resist the torque then the rear drive shouldn't suffer. In drag racing and oval track racing where traction is everything it is a different story.
Having said that I would built a good quality rear but not overbuild it and lean more toward insuring good lubrication for the anticipated speeds.
