Man, don't know where to go from here. You've checked and gone through about everything. Have you checked for spark again lately? Maybe try pulling and using the plugs that are currently installed to test for spark? I've had plugs not fire before that were brand new. Looks like you have everything set up properly - aux tank, vacuum ports all capped off - etc. You've gone through the carbs but like others, if carb cleaner shows a spark of life, then it starts looking like a fuel problem again. Good luck. Later.

Do a compression test. Has the valves ever been adjusted.