That body is way too small for a 13” wb rig imo. Also I would use styrene to stretch a hard body but not a lexan body. Too much flex...I’d keep looking and keep my mind open to different bodies. But most of all I’d wait until you have the kit on your bench and can take some measurements.
Any of the Proline 1:8 monster truck bodies would work, most of the Jconcepts scaler bodies should but the detail sucks imo. Personally I’d get the Son of a Digger body and call it a day, it is rad. Then when u get bored of it change things up. I’ve even seen a Jconcepts Creep body on an SMT10 and it looked decent. But those smaller Jconcepts bodies look decent at a glance but stare at one for a minute...totally out of scale to the cage, axles, wheels...no thanks. Maybe on a WK or similar but you need a bigger body on your 2 choices I think.
Google “Big Merica monster truck” and look at what that guy does with the Proline C10 bodies...outstanding. He started on SMT10 chassis and now runs them on full custom tube creations and they look very real.
Also look in Scale Builders Guild, search for “The Crusher”, it’s an SMT10 shortened to 12.5 with the 80s Chevy body 12.3 wb and it looks freaking awesome. It’s the build that made me want to do a scale MT.