Aftermarket Air 69 Dart 340-6pak

not sure if the toilet flush thing will make a diff , just a thought!!
If i was you i would put another spacer on the long bolt on the ac compressor so its good , solid and tight , any amount of flex in those brackets may cause issues
Then i would run it around with the air con turned off and disconnect the clutch wire just to be sure and see if the problem is solved .
if all is good with the compressor not running , re connect the clutch wire and see what happens with the ac running .
If it throws the belt then , you can start to investigate an air con problem .
try a new belt on the alternator side and see how it runs , maybe the old belt was on its last legs anyway and if they are on the way out , running an adjustor like yours on the back of the belt might make it fail sooner rather than later.

let us know how you go
cheers
ben

p.s that picture of the belt half off the adjustor is not how it is , is it? if so thats a fail .
Im sure you wouldnt have it like that , would you?