I've seen this a lot and it's common on a lot of the newer batteries being produced.
The original batteries came with threaded holes, a lot of the current batteries don't.
When the lead is cast, it is only cast with some bumps that catch the thread of the bolt and this allows for the bolt to cut its own threads.
The problem with this is quality control isn't what it used to be and even with a new battery is very easy to over torque the bolt and now you have a poor connection.
Most your do-it-yourselfers and many new mechanics don't understand this so they just keep tightening the bolt and when you do that any of the threads that you cut actually get pulled out.
I'm not saying that's what happened in your case but with the negative cable being loose the battery will not properly recharge as you drive the car. So it's possible you have enough juice to start the car you drive it for a while come out a little bit later or the next morning and the car won't start.
This is because with a negative cable being so loose the battery didn't recharge. So basically what you did as you were driving, is you were running completely off of the battery just the same as having a bad alternator. The HEI system doesn't need a lot of amperage and the ECU only needs 10 volts so as long as it's getting that, the car will run, plus your alternator is working so it never trips the warning light.
Yet, the minute it doesn't keep running, the car will quit and as you find out, it also won't restart. And all of that is due to just a bad ground because ground cables lose.
A dirty shop will sell you a new alternator and battery, and you be none the wiser.
If you find this problem in the future all you have to do is just Helicoil insert into the battery which is 3/8 x 16 NC thread.
On the cable being too tight this should not be an issue because even on a normal car the engine moves as you drive it which means the cable has to have a certain amount of slack in it. If it doesn't like in the case where the cable barely reaches the battery it will pull the cable out of the battery.
On the other issues check fuses and grounds, your dealing with old wires, things get loose and corroded.
On the fan issue everything works on the ground side. This is counterintuitive but the switch grounds the circuit for the fan. So when the fan is on low the voltage goes through a high ohm rated resistor wire that needs air flow to keep it cool otherwise it will burn out. This is all found in a resistor block that is mounted right next to where the fan motor is mounted. When the fan is running on high the fan motor is fully grounded and this allows the fan to run at high speed. So once the other things are checked check your resistor block. If those coiled resistor wires are burnt or broken then check your fan motor because that means your fan motor is starting to go out.
