15x10 backspacing

[M1A1TankerTom]

I am starting to look around at what wheel/tire combo I will be running on my truck. I have a 62 fleetside with a what i believe is a 67-70 disk break front end and rear end. My truck will be lowered 4 in the rear and 3 in the front. I want to run 275/60/15 tires on a 15x10 wheel in the rear. What backspacing should I run to make this fit my truck. From what I have researched im thinking 4.5 backspacing should work but I wanted to throw it up on the forum and see what you guys think.

Also what do you guys think I should run on the front? I would like to run 275/60/15's on the front as well but i have no idea if i should try and fit them on a 15x8 or a 15x10 wheel, and have no idea what backspacing for the front.

I am mostly worried about the rear backspacing right now but would also appreciate any help on the front as well. Any help is appreciated. Thanks.