1969 Dart tire & wheels qustion

Welcome and very nice GTX ! My sons Dart you see here has the stock wheelwells and the springs are in the stock location. There slicks we tried last year when it still had the 383 in it are MT 28 x 9's. They are on a 7" wheel with a 4.5 backspacing and they just fit. Cant go any taller without stretching the wheelwell and cant really go any wider so he should be able to fit that size tire. We plan to try them again this year with the new 400 in his car. I figure Stockers have dipped in the 9's on 9" slicks so they should work. :) Ron