The buttons are used as "spacers" in between the two axles once they are assembled with stock bearings. You need them to be able to get the proper axle end play with your adjusters.
When you remove the axles, they might fall out into the housing. If so, just clean them off and find a spring pin to fit them together, and put them back in.
The pin just helps keep them together during assembly of the axles.

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1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)