Hi Jack and welcome to the site!
You should really start a new thread and put your specific issue in the title; works best in terms of attracting eyes that might be able to help…..and is generally considered good forum Etiquette.
Your problem can only be one of three things; spark, gas or compression. I suspect spark and I would ask how you are testing it. Generally you would want to verify that your spark can jump a nice healthy gap….maybe twice or even three times the 0.35" gap at the plug. This is best done with a spark tester like this one:
If you have good spark with this test I would then remove the plugs and squirt a bit of pre-mix directly into the cylinders and try starting again. You can also inject pre-mix in the throat of the carb. You might have to remove the silencer part up front to do that.
I’ve had sunken engines too….and I generally inject liberal amounts of pre-mix down the throat of the carburetor with the engine lying on the ground so it runs in past the reed valves and into the crankcase. Turn the engine over for a bit to get the fluids to penetrate and displace any water that is in there.
You can do the same through the spark plug holes…..again with the engine lying on the ground but with the cylinder head facing upward.
Why not start a new thread and see who else replies to you. Many of us have been there and sure don’t want a fine engine to be damaged by rust. Hopefully there wasn’t a lot of sand or mud in it’s resting place.
Good Luck!