The problem with bringing back any legacy system is supply. There are literally thousands of parts in something like an airplane. Even if you have all the technical specifications, the vast majority of those parts are no longer available and the companies that made them no longer exist. The tooling to make specialized parts has likely been long thrown away, destroyed or lost. (I have been involved in reverse engineering legacy systems and, mostly, they have to be redesigned and that is not cheap.)
Planes built today are designed for the add-on systems they will carry, which is much cheaper than trying to retrofit those sensors and weapons into a spot that was not designed for them. Also, piston planes require a type of gasoline that is forbidden by the EPA. (Not to mention a host of other issues that make piston engines more problematic than the far superior turbine engines that replaced them.)