Another ET guess...

24-in tire that's pretty vague description 24 in 10.5 drag radial would hold a lot of power, I ran 265 50 14 years they came in at about 24 and a half inches and you're right with the 391 it factors into close to a 430 but when you start hitting it with torque in a bottle that's a whole different story. You can probably tippy tow your way into the low 12s just my guess.