Super 55 (gas) won't fire

I have a gas Super 55 that I bought a few years ago in running condition but didn't use much and gave it to my brother for awhile, but he didn't use it at all. When I gave it to him, it "ran when parked" but sat for a few years without running. It was shedded for a time, then moved (not running then) and sat out in the weather for a couple years. I am now trying to get it running, have yet to hear it pop or fire. It turns over just fine although the starter seems pretty sluggish, running 12 volts which may have been converted from 6 volts at some point in the past. Over the past couple of months, at a cost of several hundred dollars, I have replaced spark plugs, plug wires, coil (12 volt, internally resisted), points, condenser, rotor, distributor cap, ignition switch, battery cables, and even the carburetor (replaced with a new one from YT), and also cleaned out the air filter from top to bottom. I have spark at all cylinders but it will not fire, even with starter fluid at the intake. Most recently I reset the timing manually using the technique outlined in the original operator's manual, but still no action. I am starting to run out of ideas. Any suggestions would be appreciated.

#1 trouble shoot then parts NEVER the other way around or you can add to the problem.
Since it has sat and not been run very good chance the compression is low due to sticking rings and or valves. I'd fill the cylinders with ATF and put the plugs back in and let it sit a week or so. If it has a vertical exhaust I'd pour as much ATF down that till it starts leaking out. Then after a week or so pull the plugs and spin it over and then try to start it.

Takes 3 thing to make one run. Spark fuel and compression

If you have gas and spark, I'd get some help and tow it.

needs air, fuel, spark, and compression. air needs to have sufficient volume, meaning no obstructions, fuel needs to be in the right proportion in fuel air mixture. the right fuel/air ratio can be pretty flexible in just getting something to run and fire. fine adjustment can be made later. spark needs to be hot and timed right. compression needs to be sufficient to light fuel/ air mixture. if one goes thru each of these one at a time you will get to the problem.