1973 Scamp ?

Tires are so important but not easy. I have a 1973 scamp with an 8 3/4 BBP rear end that was narrowed to 49.5 inches. I have the SS leaf springs moved in by 1/2 inch with Dr Diff relocation kit. No tubbing done at all. The shock plates have 1/16 inch space from the brake backing plate. I safely have 4 inches from the wheel mounting surface. This means my backspace will need to be small, about 3 inches. What is the widest tire size that will fit for the rear only?

I am speaking about section width. Can I get 265s or 275s on a 9 inch rim?
Is 27 inch the tallest in this configuration?

Surely I will need to get a specific wheel with the correct backspace.