40+ PSI boost just seems insane to me on a car like that but then I don't know whats under the hood but on that car with stock motor I wouldn't push it past 18...
Tex I'll bow to your greater knowledge on this as I'm sure its possible
after all stock Mustang block is rated to 500HP.
As for why I'd say as the bolts hadn't been torqued he dropped the clutch, they sheared he bought the clutch back up and it came up sideways....