The fuel line near the pump might be a low spot and decent enough to somehow get a good portion out. I do miss a 440 mopar cop car that had a T in the line (to assist motorists?). Not that I'd encourage risky things but the engine could be run from another source if already drained low enough for the pump to do the rest of the work.
The siphon will get enough of it out. No additive necessary, just fill the tank with good gas. My plugs were even worse than yours, they were pitch black. My plugs were in there for a year before I started my car for the first time since I stored it. I noticed it wasn't running right, the exhaust was smoking, and it just felt sluggish. When I pulled a plug, it was black. My MSD ignition managed to fire it, but once I drained the gas, replaced it, and the plugs, all was well. If you are using points, you'll want to check the dwell. Worn points will weaken ignition and make things even worse.
