The two things that make or break an airplane are the engines and airframe. Everything else can be swapped out. As long as the airframe can support the engine, structurally and aerodynamically speaking, there are no issues. Wiring and avionics can all be easily replaced. The control systems for the plane can be reworked too.

GP is correct, this is a plane designed almost pre CFD, a clean sheet design would go much further than this. They are missing out on half a century of material science advances.