The problem with C-body axles is that they have a necked down section after the spline, so there's nothing there to machine for extension of the spline. If you were to use a C-body axle and cut the spline in from the point where the larger diameter is resumed you finish up with axles about ¾" shorter than the A-body axles.
This is why I mentioned pickup axles, they don't have the necked down section for some reason.
There is another way to overcome the brake maintenance problem (if that is your issue) without even removing your axles. You cut off, grind away and belt out the studs, throw away the drums and buy later B-body drums, go to the wrecker and get studs from later model Mopar vehicles fitted with 8¼ or 9¼ rear ends.
Or do you want the flanged axles because you think the tapered ones have a problem?