OK, well that gasket you found is the gasket that is between the fuel pump and the crankcase, have you had the fuel pump off lately? The engine probably wouldn’t have run too well without that gasket in place, so I am thinking someone had the fuel pump off previously, replaced the gasket but never retrieved the old gasket out of the engine pan.
Those "surface gap" plugs are no longer recommended for your engine, they tend to foul easily. I would replace them with Champion QL77JC4 plugs gapped at .030".
That little puddle of fuel in the pan isn’t too uncommon, especially after cranking excessively on the engine when it wouldn’t start. There is a little round gasket that fits between the air box and the carb though, look for it to be stuck into a groove on the air box. Be very careful when reinstalling that black choke knob, it will fit in place two ways, but only works correctly one way. If installed upside down, the choke won’t close fully when the knob is pulled. Be sure to push the air box tight against the carb before tightening the air box screws/washers snuggly.
Now, back to the original problem, the engine won’t start. First, I would check for spark, have you done that? Do you have a spark tester? Don’ t forget the new plugs. The engine should be able to jump a 1/2" gap while cranking, but am guessing you do not have an actual spark tester. Please be very careful when checking for spark, clean all the gas from the engine pan, check spark in a well ventilated outside area.

Well, I hope it is just the plugs….Try to check for spark while replacing the plugs…Don’t think the gas went bad, but it is possible that it sucked up some water from the tank…I don’t see any water droplets in the puddle of fuel in the pan though.
Please remember to get that choke knob properly installed or the choke won’t close fully….

Sounds like your hooked now. 😮
Better go buy a bunch of lumber.
Your going to need a bunch of motor racks soon ❗
LOL

Steve A W

if it works don’t fix it anymore !