m/t sportsman tire heigth

what size tire should i run? i can fit 29/12.5/15. mini tubbed. about 450hp i think. 1970 scamp, 3500lbs,340- 10/5 to 1, pop-up hyperu, closed chambered heads (thick gasket) air gap intake, 750dp, lunati solid cam 60433, ported heads from brian. shift at 6700 to 7000. 430 posi 8 3/4, 727 reverse body, 4000 stall (brakes only) do not want to go under 11.5 or i need rollbar.
Thanks:prayer: