Hey Sebastian,
Great project, I look forward to staying tuned!
About a year after I bought my 83 (way back when) the rear-end went caboom (with just 28K on it, thanks probably to the first owner being really hard on it or maybe just one of those things). So, I replaced it with an 85s that my mechanic said was a much better transaxle, and the synchros were certainly better. I put another 150K miles on the car until two years back when that gearbox gave it up - I jumped at the chance to get the original 83 back in! With all the mileage I put on the 85 transaxle I still always found myself wanting to grab 6th gear - now with the 83 back in it is just right! I really don't see the advantage of the 4.10 especially when you have the additional horsepower - with the 3.4 you can still cruise at 65mph in 4th if you really want to stay in the powerband, but what is so nice is grabbing 5th, the revs drop, and the car really quiets down. With the LSD I can't think of a better match up
I'm jealous on that trick!
If there is one problem it's that it is very easy to go very fast
so check those freeway on-ramps for the highway patrol as you go!
Cheers!
GV