Back spacing with disc and drum brakes

[Rusty one]

I'm starting to search for some wheels for my 63 C10 with front disc and rear drums. I'm looking to run 215/75/15 up front on a 6 " wheel and 235/70/15 rear with an 8" wheel. ( 6 lug wheel)
The truck will have full air ride with the ability to lay frame.

My question is ...what back spacing will I need upfront to clear the disc brake combination? I'm thinking 4" b/s in the rear,but not sure up front.

Any suggestions will be appreciated.
Thankyou