You can make the car as slow as a turd or so fast you kill yourself within a 2 seconds.
69 Mustang would be capable of reaching well above 150 MPH and still save streetability. IF you really want you could push the car over 200 but you are talking about some serious modifications to achieve this. personally I would track down a 428CJ. 69's reallly really have a cool Factor to them and leaving one stock is only a good choice if it was highly desireable to begin with. A "Molested" car that originally had the I6 but now has a souped up Year/Style correct V8 Performance engine will be worth more than a showroom quality exact replica of the car how it came from the factory. From the
ford parts news and ford cars experts the people who are BUYING these cars and of are the ones that wanted them as a kid but never could have them. I don't think anyone drooled over an I6/3 speed but if you turn it into a "Clone" Car someones gonna be interested because its close enough to satisfy the drolling their tastes desire.