zoera, a lot of folks were VERY unhappy when they realized their "247" (
) was actually a 428. Or so I've heard. It was quite a big deal early on. Rumor has it Shelby replaced some 428's with a 427, sweet heart deals for a select few perhaps. Others pulled the 428 and installed the 427 themselves.
Pro or Con? I really don't think it carries much weight either way, depending on what the buyer is looking for. A buyer looking wanting a 428 just because thats what it came with would be a rare duck I think. In THAT situation the car itself would need to be restored to very exacting standards all the way around.