F23 never came factory with LSD, many claim it is better if not at least as good as the F35 for handling torque without failure. There are so many F23's out there compared to the 35 is one reason several of us are making the move in that direction. It so nearly impossible to source parts to rebuild a F35 and the process is exceeding complex as compared to the F23. New 0 mile F23 can be purchased for 500 add another 1000 for a quafie and you have a nice 1500 mile 0 mile Goblin manual. A rebuilt F35 quafie can run you 5000 now days if you can source it. F40 is another option but you need frame modifications to use it in the Goblin and it will cost a considerable amount more. Not sure about F40 but limited to 3.95 or 4.05 gear ratio (I believe) in F35 while F23 has 4 options from 3.84 to 4.41. I would guess that the majority of 100k + mile F35 trans are starting to have the 1-2 shift syncros wear to the point that no-lift shifting becomes an issue.
Per GM information:
F40 final drive gear sets - 3.09, 3.55, 3.76, 3.90, 4.18
F35 final drive gear sets - 3.82, 4.05
F23 final drive gear sets - 3.84, 3.95, 4.17, 4.41
Please note some aftermarket gear sets are available that may have different ratios.
F40 gear ratios (1-6) - 3.92, 2.04, 1.37, 1.05, 0.85, 0.74
F35 gear ratios (1-5) - 3.38, 1.76, 1.18, 0.89, 0.70
F23 gear ratios (1-5) - 3.58, 2.02, 1.35, 0.98, 0.69