Make up two 7/16 or 1/2 inch jacking bolts, put them 180 degrees apart between the axle flange and backing plate. Then, go to it. It probably just has a bit of rust and some grease that has turned to glue. When you get one out, you can drive the other out with a piece of pipe or use the jacking bolts bolts again. The retainer bolts have to be removed from the housing - don't lose 'em as they are hard to come by. I am using a '57 9" that probably had never been apart. The jacking bolts worked just fine.

I hate to disagree with anyone on these threads, but heat can warp the axle tubes.