Very cool project. These home brew mods are my favorite and stretch chassis projects are always fun, I've done a few myself. Love your 2nd version of the rear shaft.
You know your new wheelbase should be pretty close to the wheelbase of 1/5 and 1/6 bodies from FG, MCD, Redcat, etc. Just an FYI in case you want to consider alternatives to 1/8 bodies.