Stuck driveshaft is very common and tricky to save. Often times when you pull them out the crank splines come with it. Older ones hold up better.
I use a flare tool and a c-clamp to grip the shaft and then rig up a expander to that. Penetrant and slight tapping helps. I usually do it over a...
Maybe...is that a false hollow bottom? Anti cavitation plate should be even with the bottom of your motor is clamped to the transom, higher if it's on an offshore bracket.
Why would you not run some kind of corrosion blaster through your motor when you haven't even diagnosed your motor. Nasty looking t-stats tested fine, right? The water orifices in that motor are not very big...plugging is easy.
That motor is not ready for fishing.
I couldn't find that part for your motor but maybe I missed it. Is that your cam roller for the throttle? If so, it should go on or not. Sounds like you have the wrong one.
Lower Unit (LW) will need to stay in the water at all times. (For over revving and coolant water/lubrication) If your using the existing transom and not on a plane the water should be quite high so I wouldn't think it would be a problem. And like Racer say's, aftermarket adjustable brackets are...
Brandons garage shows you how to install one and lists the part number (YouTube)... Any parts motor will have one... Cdi electronics probably makes and sells one. I have many...dime a dozen really. Pretty sure the only thing you don't have is an overheat sensor so you won't be using that wire.
That's the older one. Either buy a vintage harness or they sell a replacement harness that converts it to the red plug. More wires, more options and not hard.
Or I make my own with aftermarket connectors.
Crosbys example doesn't work for your motor but it's what it could be.
You can look up...
No key is needed. Unplug the motor and jump the starter solenoid. Spark gap test of 3/8 or better while checking compression numbers.
Easy to do and gives you a wealth of info.
Post the results.