Help me confirm my measurements and back spacing thought

70Roadkill said
i have a 1970 Dart Swinger, 8 3/4 rear axle, dr diff big bolt pattern axles, and I installed a 3/4" offset kit.

When I measure from the drum surface to the outer wheelhouse lip it's about 4 7/8" and from the the drum surface to the spring I get 7".

My plan is to is to get a 15x8 rim and put on a set of 275 60 15 tires.

I'm thinking I need a 5" offset to make it work. Can someone chime in to make sure my math is correct.

Thanks

Just taking a few steps back on this....

Is the rear a small bolt A-body rear you just put dr diff axles in and moved the spring in?

Do you know the outside drum face to outside drum face distance?

Trying to determine what basic axle housing you have.

Did you mini tub your 70 Dart? You should hit the inner wheel well before the spring.