You did have the right idea. Disconnecting things, one at a time. I guess by RPM gauge you mean a Tachometer? Disconnect that. I am guessing it's a stuck VR so buy a 10si alternator and install it. Throw way generator, VR and all it's wiring, Get rid of the ammeter. We can help you install the alternator and a voltmeter. This will get rid of a lot of trouble you are having and future troubles, for very little money. If there is a draw after that, we will help you find it. But with what you have now, it's too much trouble. Save up for a Painless or Speedway 12 circuit harness.
As you know, I've already recommended much of this back on Feb 19 at post #1398028 of your post.
I know I have given you advice you didn't ask for. You just had one question.
To actually address your post: After your story about various issues, you only asked one question. "If I wanted to run power to the coil/ignition would that be a simple matter of adding a new wire from the key to the distributor?" This is easy to answer but difficult as to which way to answer. Keeping in mind you are not good with electrics.
1. Disclaimer: You have a swapped 261 motor and now have 12V. I do not know what wiring was done by previous owners and by you. A stock 49 would have had a 216 or 235. I will assume you have a foot start with an on/off type of switch of some sort. I do not know of any accessories that may have been added to truck's electrics.
2. Stock 49 would have battery cable to starter button stud. The type of starter button used for 12V. It has a "side terminal". This button is mounted to the starter and is actuated by the foot lever.
3. You should have a ballast resistor on fire wall (white ceramic block). In your case, there should be two wires on coil positive. One from the starter button side terminal and one from one side of the ballast resistor. Then a wire from other side of ballast to Ignition switch "ON" terminal. (that terminal probably also has the gas gauge feed wire)
4. Back to the starter button stud: There should be a wire from that stud to one of the ammeter terminals. Then a wire from the other ammeter terminal to the ignition switch battery terminal.
Check to see all the above is wired like that. No other "wild" wires. No miswires. If you see something wrong, stop! and Report. If all looks good, then with ign sw off, check to see if ign sw batt terminal is hot, If it is, turn switch to "ON". Check that it's "on" terminal is hot. If it is, check that coil positive is hot. Turn off switch. Check for draw after switch is off. If you have a draw......
Take negative battery cable off of battery post. Take off battery wire on VR. Tape it up or tie it up away from anything. Put battery cable back on. Key OFF. Check for draw again. If you still have draw. take off cable again. Install VR battery wire. Report. If the draw goes away, it's the VR. Maybe generator brushes. I'm not sure. I don't like, or use, generators and VR's so don't I want to know about them. They are worthless, unnecessary electrical headaches.
BTW the answer to your question is NO.
