Just FYI, I recently obtained my father's 1991 C3500 (7.4 TBI) and I plan on installing a Santa Cruz radio. Santa Cruz offers a direct replacement for the older OBS trucks that have Bluetooth and such. looks stealthy and is modern day. https://www.retromanufacturing.com/
You could disconnect the throttle cable at the pump to ensure that the cable moves freely through it's shielding. Other than that, I think you answered your own question with the shaft difference and pull angle.
Or, you could leave it and that would keep your son from straying too far from...
I used to have issues with my battery cables coming loose and when they did the ECM (computer) would not work and the engine would have a loud rattling sound, it was timing I suspect. Once I fixed the cables it was fine. So, what I'm saying is maybe it has something do with your ECM.
Best of luck
There's not enough room for an Allison without doing at least a bodylift. I saw one a long time ago done and I recall a body lift was needed. I'll try to find the article.
I think Big T has a good point which I didn't know there was a solution. I'm going to take a look at Twisted Steel for that steering shaft. Re: "heavy feel" some trucks have a speed sensor on the backside of the power steering pump. This regulates the amount of assistance provided by the power...
No, skids plates are to protect the front drive differential and the transfer case. The "C" indicates two wheel drive while the "K" indicates four wheel drive.
Any codes present? What's the VIN i.e. F or S motor. I've had issues (S vin) with the mass airflow sensor in the past while using a K&N air filter. If so, sensor can be cleaned using carb and choke cleaner. I now use a regular cartridge air cleaner.