When I put 16 wide under mine, the tightest spot in the tunnel was the tunnel reinforcment brackets, I removed them and put external braces on the footbed and tunnel, works fine, can get them from an MXZX model or from the aftermarket such as Specialty Sleds.
With a 156x16x2.5 I'm running 7t extros and 19/45 gears with stock chain(have to remove idler in chaincase to install chain, then reinstall).