If you now have the 8V-71, why not rebuild them to turbo specs and do what I did and change it to turbo and air to air intercooled? If you hop up a 6V-92TA and go to 100 injectors, that's 600mm injection per rev-and that would be putting alot of stress on the engine. If you hop up a 8V-71 with turbo and air to air intercooler and go with a conservative 80mm injector, you get 640mm injection per rev, and that was a factory setting by Detroit that put out 400hp and 1200lb/ft of torque. Go to 90 injectors and you're getting into 8V-92 performance country from a 8V-71, or 450hp and 1350lb/ft of torque-of which you'd have a very short lived 6V-92, if you tried, but the 8V-71 can take it. Just saying you can get alot of power out of a 71 series as compared to the 92. The 71 is just a more robust engine and alot more forgiving. I took mine from 65mm injectors that were 300hp and 800lb/ft to the very conservative 75mm injectors with air to air intercooling (custom made to my design) and now have 375hp and 1125lb/ft of torque. It changed my 6% long hill climbing from 30mph to 40mph pulling my car, don't hardly have to down shift, and actually have some passing power now. With a good 13 spd, you'd be in hog heaven. I personally don't like the 92 series since it has wet cylinder liners that can leak into the crankcase, whereas the 71 series has dry liners that are almost impossible to leak.
On the Roadranger transmissions, they make reverse shifters for bus use, at the transmission. Personally- I'd go with an Allison- no manual transmission can come close to the around town acceleration, and the pure enjoyment of not having to shift constantly-and this from a truck driver that drove nothing but 13 spds for 21 years and 1.3 million miles worth. If anything, put in a 10 speed Autoselect transmission (Autoshift that works with mechanical engines-only difference is that you have to work the throttle between shifts). Good Luck, TomC