There was another post about this recently. The fourth plug on the temp, oil, ammeter plug should provide 12V keyed power. Worst case you can use the hot side of the coil until you run another line from somewhere. You also need to plug the hole going to the choke that once housed the hot air line.
My 72 had a 12V keyed source available but I ran off the coil for weeks without issue. Note that it will likely drop your voltage on the coil down.
You'll have to plug the exhaust manifold hole as well. I used a bolt from home depot that I hammered it. I bought 4-5 bolts which all seemed close to the right size then picked the one that seems just a little too big. Note the hole is larger at the opening.
If you have an electric fan like I do you'll also need to find a keyed 12V source for that as well.