What backspacing works with a 10 inch wide rear wheel and Porterbuilt dropmember

[G-NUT]

I have a 1985 fullsize GMC 2500 that I'm converting to 1500 / C10 rolling attire.

What backspacing works with a 10 inch wide rear wheel and Porterbuilt dropmember without having to narrow the rear axle?

I'm looking to run 24" wheels all around; a 24x8.5 on the front and a 24x10 in the rear.

I already have the complete Porterbuilt Level 3 front dropmember and McGaughy 2.5" lowering spindles. The complete Porterbuild Level 3 rear dropmember is on order. None of which is installed yet.

When the time comes to actually order the wheels I do plan to get the truck up in the air and do some measuring. I just thought I'd get some idea for now.