I spent the last 6 hours on gt40s.com researching the audi trans and it finally hit me that I have an 013 instead of the 016 that they all seem to use. It doesn't look like the V8 rear diff is an upgrade option for this unit......at least not that I can tell. The only folks who are using the 013 are VW Fox and Dasher enthusiasts.
I wonder if the Peloquin Pelo-lok 80% kit would work on this differential?
Aftermarket cable shift setups for 911's and mid engine porker trans kits have given me plenty of ideas for how to convert to cable.
Off to look for a cheap flywheel. 
I have some points you should look into, my boss is a formula vee/ beetle transmission specialist, this info might be relative..
Running it backwards in our transmissions is difficult because the synchro rings are cut to lock with the slider on acceleration, and off load the cut on the other side of the teeth aren't cut as aggressive, this is why it is easy to take out of gear without clutch use on decel..
In the vee we have the transmission totally backwards, mid layout vs rear layout, and still retain original shift pattern.. We use the shift rod , just as the original beetle, but our shift pivot is below the shift rod on the lever..
