I'll attempt to address these one at a time:
First, a large, roughly 4ga cable from battery POS clamp runs down to the large starter solenoid lug. Ideally it should be red to denote the positive side, but yours happens to be black...so be it. That one is correct.
Now, while we're down at the starter solenoid, we should see two additional wires connected to that large terminal. I'm saying should, while recognizing that might not necessarily be what is currently there at the moment. One of those 'should' be a light blue 10ga wire that travels up and across the backside of the engine and then passes through the cab via a firewall bulkhead connector on the driver side, then terminates at one side of your ammeter gauge. The third wire attached to this large solenoid terminal should be a 14 gauge red wire that heads up the back side of the engine, makes a right turn and runs vehicle forward between the intake runner and the valve cover before dropping down to the alternator #2 terminal, where it splices to the short red wire of that two wire pigtail. There should be no fuse in this circuit. What I see from your pics does not fit my description of what the red wire is supposed to be doing. What I see is a red wire passing through an inline fuse on the fender. That is incorrect.
Now that we're back at the alternator, we have a 10ga light blue wire that should also enter the cab via the firewall bulkhead connector, terminating at the other side of the ammeter gauge. That's right, (2) light blue 10 ga wires, but in essence they are actually the same very long wire that is being bridged by your ammeter gauge, thus creating a big loop between the alternator B+ stud and the battery positive terminal via their shared contact down at the large solenoid terminal.
Now, I'm glad at least that the purple wire between the alternator #1 white wire and the small gauge brown with white tracer resistor is creating a circuit. The splice between purple chunk and resistor wire sounds pretty sketchy by your description. I'm wondering if there is still enough remaining length in that small brown/white resistor wire, that if re-routed in a more sensible and direct manner removing any unnecessary loops and whoopdee-doos, could allow one to splice it directly to the white pigtail at the alternator #1 terminal, thus allowing the permanent removal of the ugly purple chunk. The ideal scenario there would be to have the brown/white wire connected directly to white Alternator #1 wire without stretching or binding it. The fewer splices the better on any wire, not just that one in particular.
Now let's talk about resistance values, because we need to clear up some confusion that you have. The value of that brown/white resistor wire is not 1.8 ohms. That's the value of the other resistor wire in your harness. That's right, not one, but two resistor wires with very different values and very different purposes. The other resistor wire that is supposed to have a value of 1.8 ohms is the odd looking, cloth insulated wire that terminates at your igntion coil positive terminal. It's job is to step down the voltage going to your coil and your distributor breaker points set to keep them from overheating. I can see from your pics that wire is still present, but has a non-factory ring terminal on it. That by itself is no issue, as long as the length of that wire was not significantly reduced when the new ring terminal was added. The 1.8 ohm value in that wire is achieved by 72 inches of wire length between the bulkhead connector and the igntion coil. That's far more length than is required to complete the span. What the factory did is fold up the excess length of that wire back and forth and back again and then wrap the folded mass up in electrical tape. What can happen through ignorance later on, is someone trying to clean things up and replace failing connectors, sees this ugly mass of a much too long wire for the run and decides to snip off the excess length of that wire, thinking they made things better. Ask me how I know about this one. What that does is reduce the resistance value of that wire to the point that it isn't adequately stepping down the voltage to the coil and the points. All of this is aside from your charging issue and my advice would be to not concern your self with the wiring to the coil right now, but rather focus on the charging system wiring between alternator and battery and all points in between until that has been satisfactorily resolved. The engine is starting and running at this point, but your battery is being depleted instead of being replenished, so that is the fish to fry for now.