1964 Dart Owner - In Over My Head

You are way ahead since a nice body and paint. Your issues are minor and common (at least until you snapped the manifold studs). Common parts are easy to get and cheap. Check rockauto and ebay. I recall paying $15 for the tank filler grommet (coat w/ vasoline to slide in the filler tube). Even a new tank is only $100 and stainless level sender $45. You will find most basic parts to be much cheaper than for a new car. I just bought a set of spark plug tube seals for $0.45 on rock (clearance) and earlier got a 904 transmission rebuild kit w/ steel plates for $50.

Re removing the broken studs, that is always an adventure. If you remove the manifolds, there might be enough left to grab. But, you only get one chance so don't wing it. Vise-grip pliers might work, but a good Craftsmen set of "stud removers" might be smarter. Soak the threads for days w/ PB Blaster. Heat the studs w/ a torch, to red-hot if possible. When you try to loosen, first go in and out while spraying more penetrant, the goal being to free and flush out the rust which is locking it. Tapping the end of the stud w/ a hammer also helps by hydro-shocking the penetrant to free rust, but only works if the penetrant has gotten deep into the threads. Of course, replace all studs while at it (preferably grade 8) since you proved they can't be trusted. If broken off flush, you will probably need to remove the head to take to a shop. They remove those all day long, sometimes even using a "tap burner" which electrically vaporizes the metal stud. But, before pulling the head, first do compression and leak-down tests to tell if you should do a ring, valve, or rebuild of the engine. With the head off is the perfect time, and a re-ring & hone can be done w/ block in the car. If you measure >130 psig compression in all cyl, plus feel each cylinder resist strongly as you turn the engine over by hand, no need to pursue that.