Someone please help me

Need a LOT more information here-
What ignition are you running? Chrysler electronic, points, MSD...?
What fuel system? Mustang high pressure EFI system or a fuel cell and mechanical pump? Any pressure regulator/fuel return?
Too many variables to diagnose with the little bit you've given us. So much depends on how you swapped it- how it was wired, how the fuel was plumbed, how the throttle and kickdown are hooked up, etc.
And yes, those two little screws are for idle mixture adjustments.