I think they would fit fine. I say 11.5 you should be able to put on there . I know alot of people run 26x10.5's on the stock pony wheels which are only 7" wide.
yes they will fit, i used to run M/T slicks in 26/10.5/15 on a 15x8 draglite and then went up to a 28/11.5/15. The 28 will fit good, except in the wheel well, i needed to trim a little of the plastic ground effects inside the wheel well so the tire wouldn't rub, the 27 inch should fit without trimming.