Rebuilding A '62 Pickup

HELLO ALL,

I'm new to this so please bare with me. I'm re-doing a '62 chevy pickup. It's a custom short bed stepside. I want to replace the rear lugs from 6 to 5. Do I need to replace the whole rear axle, or can I just replce the hubs ,or each individual axle? And how do I tell what size rear axle I have? I would appreciate any information on this subject.