First rule of internal combustion engines: If it has fuel, spark, and compression it will run, maybe poorly, but it will run.
Sounds to me like you identified spark as a problem. Clean all the grounds and inspect the coils. Make certain that the case is well grounded to the frame. You must have metal to metal all the way. If you have any paint under a ground strap it is no longer a ground strap. See if you can find an inductive timing light and put it on each plug wire to see if it actually sparking.
Next check compression. If you don't have much compression you could be off by a tooth or two on the timing chain. When the Guzzi specialist looked at it did he pull the timing cover off and look? When I timed my engine recently it was pretty simple but I did actually put a dial indicator on a cam lobe to verify it. Easy to be off by a tooth.
Good luck. When it finally fires up you'll feel great!
Edit: I didn't read the last two pages. this is mostly redundant, but make sure you check the grounds between the engine and the case.