Sounds like it is safe to assume you have spark and compression, but fuel is not getting to the cylinders. A quick test of all that is to pull that FPR vacuum hose off of the manifold and use the port to squirt in a bit of carb cleaner, starter fluid, or other flammable substitute for fuel. You could check for wet plugs, but this is just faster.

I think it will try to start, then falter, proving no fuel.

Jumping the relays with the 5-7 is not quite enough to get the power to the ECU, although, yes, it will activate the pumps. This sounds to me like one of three possibles.

1) Blade fuse wiring near the battery (corrosion).

2) Fuse #12 corrosion.

3) AMM died.

To verify #1 and #2 in one fell swoop, peel back the boot on the AMM and probe with a test light at the orange wire, with the key on. Lack of juice here will be either #1, #2, or both. To test just #2, probe the right side of the fuse panel at fuse #12.

To verify #3, try starting with the AMM disconnected. If the AMM is bad, you should get some action.

If I'm dead wrong about no fuel, and it is flooded (you mentioned washdown!) it could be the original harness has broken off at the engine coolant temp sensor. I doubt this very much. I think if you're in this hemisphere, it is cool enough to cold start flooded, or you'd be smelling the fuel something awful.
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Art Benstein near Baltimore

By the time a man is wise enough to watch his step, he's too old to go anywhere.