I have Draglites on my untubbed '73 Duster and can only get 8 x 15 (275/60/15 rub slightly) with 3.5" BS (to actual rim edge) rears on mine, but I have a Ford 9" and not sure of actual width compared to 8 1/4.
In New Year will be researching how to tub it etc to see how much wider I can get.