Don't you dare start making better life choices now!3 Better Life Choices
I had actually wondered how good a tow rig a 135" body mounted on a 177" frame would be. The 5th wheel would still need to be ~16" behind the rear axle to provide even minimal clearance to the rear doors. With your wheelbase stretch, you'll be pretty much there.
I did not know that the 159 wheelbase was available with a higher GVW than the 177... although that may be a year-by-year thing, as the link below shows 177" available at 14,200... although that may have been rare.