Strange Pilot/ hub size on 8.75 Rear drum brakes

thanks for the input, guys!

I emailed Classic Industries about the size of the hole on their 10" A/B/E body rear drums they have available... we'll see what that yields I suppose.

I thought I would have to drill out the pattern on some A-Body drums... Rockauto.com has a lot of 9" options, but 10's are Front drums. Kinda new to the whole drum brake thing... what's the difference between the front and rear drums?