New 408 stroker runs rough at idle

Just an update, so I found that the intake gasket is leaking a lot of oil out the back side. Went to redo it, and pulled off the carb and looked inside the barrels and found the holes where the idle mixture screws are have big cracks around them, and even some of the casting has actually lifted up making the holes bigger. The guy that my dad lended it to must have over tightened those screws at one point.