Spring relocation without mini tub?

Going to be cutting my car apart tomorrow to move the springs in, and was going to do a mini tub job. The tire size I want to run is 28x10.5x15 bias drag slicks with 15x10 wheels. Figured a backspace of 5.5" would work without narrowing my rear end. I was looking at how it's set up now though, and I have at least 1 1/4" clearance between the stock tubs, and my 28x9 slicks with 15x8 wheels with 4.625 backspace and 1/4" spacers. Think I can fit the 10.5 slicks with just the spring move? Would I want to do a different backspacing?