Robert
Depending on budget and will, anything is possible. At this point, it is a bit easier since patterns are available for practically every metal part of a NG coach, from trucks to couplers to even Adlake interior parts and Kirkman lights. Authentic coaches (not just bodies on flat cars) have been built by an individual in Las Vegas, a county park in Michigan, and the Strasburg. The restoration of the historic cars at CATS has honed their talents so that if policy and funding dictate, they could build authentic cars from scratch.
Steve