I was running 31's with a BL and still had fender issues, but I was running a 15x10 wheel in the front. Little wider out back.
STX High Rider should clear 31's all day stock. Especially on a 15x7.
33's if you had a skinny wheel, but I'd go for 33x10.5. I don't see why those won't clear. Probably a little stuffed though.
I have a 3" BL and 2" in the front and mine will clear 33's on a 15x8. I have shackles in the back and I set it down on some 35's and had a little wiggle room. No flex though.
Nick Conforti - 1987 Ranger XLT - 302 - Cam - Edel Intake - Edel 650 4 Barrel- GM HEI - AOD - D28 - 8.8"- Discs - 31 Spline - 3.73 - L/S - 30" - Sony Headunit - Kicker Components - 3 12" Audiobahn 1251T @ 35Hz - HFi1000.1D Mono Class D