[427sharpe]

If by 'replica' you mean kit car, my guess is the first would be Deven or maybe Manx on a truly national sales scale. Oddly enough there is a Deven SS here in North Texas (Lewisville, actually), a 1957. Only one I have ever seen close up and it seems to be a pretty cool car..rides/handles well too!
Based on an MGA chassis, it has a later Corvette motor (327) with Strombergs and a Chebbie 4 speed. 4 wheel discs as well. All told, about 2100 pounds with 250 hp. And kudos should go to Bill Devin...way ahead of his time! The fiberglass body (replica of the original Testarossa) looks great, and finish work is very good, even by today's standards. I have also heard that Devin designed the very first belt driven ohc 4 cylinder...which is standard today.