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I just replaced the bearings and spindles on my 78 this summer. I had to purchase/rent a spindle removal&installation tool to do the job. I removed the spindle by taking off the trailing arm. This was the only way I could get enough strength with my sledge hammer to knock the spindle out. I held the whole trailing assembly in one hand and the sledge in the other. I clashed the knocker tool and sledge together at the same time in the air, in a kind of bent over position. Looked goofy but I got it apart. I'm sure there's other more safer ways to knock it out, but everytime I had it set somewhere it would just bounce badly and not get a solid hit and I was getting pissed.
There might also be another method to getting them out without removing the trailing arm, but I'd highly recommend you remove it. When it comes time to reinstall I think it's much easier setting the bearing endplay with the arm off. Also, you might find that your trailing arm bushing needs to be replaced, which requires the removal of the arm.
The reason I removed my spindles was to replace what I thought was a bad bearing. After a long time of waiting for parts to come in (and the company I orded them from thinking they sent stuff already) I found that the bearings weren't the problem. The problem was a grinding rear end. It would grind when I turned corners slowly and take off from a stop. It only did this after the rear end was warm. It was an informative and expensive process.