200-R4 transmission behind mopar stroker

I'm wondering what's the main reason why I don't see anyone running this transmission behind their SB mopars.. Art Carr builds a kit for everything you need and you get the convenience of the OD.. It's very small and would be less loss on the HP. I'm seriously considering this option to put behind my high HP 416, with 4.10 gears.. This would give me the best of both worlds.. Drive it to the track (70 miles) change tires run it, and drive it back.

Is it's b/c it's a GM product or something else? I'm not going to have torsion bars as I have coil overs up front... I'd like it to require a little cutting as possible as the interior is already complete and I don;t fell like ripping the carpet, and sound deadener up.

Jason