You are a great photographer 
Alright. My conclusion is that both the “output shaft” (axle from gearbox) and the transfer case input sleeve are worn out. This can be caused by several things but since you have the 25 spline version, which is stronger than the 18 spline version found in the early gen1 cars, it is most likely mainly due to the severe corrosion. Hard launches will also wear down splines, but this looks more like a “grinding wear” than a “brute force”. The end axle of your TC looks OK and does not need to be replaced.
From personal experience and other peoples experience, I would recommend replacing both the output shaft and the TC sleeve. Both of them are so worn out that if you replace one of them, the one you do not replace will cause rapid wear again.
There are after market shafts and sleeves which are harder than the original ones. But since you have the 25 spline version and don’t plan on dropping the clutch@6000RPM with a heavily tuned engine a regular strength shaft/sleeve will work just fine. https://www.rvengeperformance.com/ and https://www.3sx.com/ have a few options.
The good part is that both the output shaft (axle) and the sleeve are quite easy to replace. You will need a hydraulic press but there are guides available on how to do it.
If you drive the car before replacing them, be very careful if you start hearing a grinding sound or notice that you loose power similarly to when your clutch is worn out. This will indicate that your splines are completely worn out and that the the output shaft is slipping inside the TC sleeve. When this happens the VCU in the gearbox thinks that your rear wheels are loosing grip and is working to shift power to your front wheels. The transfer of power to the front wheels is reason you can still drive the car although it feels like your “clutch is slipping” and you have no power. DO NOT DRIVE THE CAR THIS WAY and if you cannot stop right away, be sure to drive very gentle. You will otherwise overload the VCU and damage it.
I have actually had this happen to me, and managed to drive gentle enough to save the VCU. Phew
Best regards,
Victor