The property you're missing for center alignment is defined the following way. I also added the line break mode you had defined on the iOS6 code:
NSMutableParagraphStyle *paragrapStyle = [[NSMutableParagraphStyle alloc] init];
paragrapStyle.alignment = NSTextAlignmentCenter;
paragrapStyle.lineBreakMode = NSLineBreakByCharWrapping;
You just place them in the attributes dictionary under the key:
NSArray *attrs = @{
NSParagraphStyleAttributeName : paragraphStyle,
...
};