Can i put a 302 engine on a 1966 mustang?
The leaf springs would not impact your choice in engine... unless you are pulling like 450 horsepower(which I doubt a 302 could do on a budget). If you are pulling that much power, traction bars would usually add more control and reduce chance of damage when accelerating.
Watch your front COIL SPRINGS though, make sure you have small block springs and not big block springs. Picking the wrong ones will make your car sit awkwardly and handle rigidly.