'57 Chevy 3200, I have replaced the drum breaks with disc on the front, and have everything mounted up and connected - time to bleed the brakes.

On the front drums (the ones I've removed), there is a bleeder valve nipple exactly like I expected to see. On the rear drums, there is a 2 part bolt in place of where I would expect to see the bleeder valve. What's going on here? Should I pull the valves off the removed front drums and install them in the rear? I feel like I'm missing something obvious, but I can't seem to find an answer as to why there is a bolt in place of where I expected to see bleed valve.

Apologies if this is a stupid question, and thank you in advance for any assistance.
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