They look a little scary but I've never had a problem with mine. 25 inch 115 E-tec on a 20 inch transom. The good thing is, it tilts way out of the water when you tilt it up.
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.