Biggest tire on 1969 dart

The rear end is a stock a bodie 8 3/4

Is it converted to LBP? If so then 15x8 with a 5.5 back spacing and a 245 wide tire should fit and may require a small spacer and some inner fender work.

I don't think you will find this as an off the shelf rim.

I had to order custom rims to properly fit my car with no spacers or BS.