The airframes designed at that time were well thought out. Every one of them could always use more power to unleash yet, more performance.
In the 60s IIRC, Piper Aircraft married a turbo prop engine to the P51 airframe. Performance was astounding. But their intended market (US military) wanted nothing to do with it.
Today there are a hand full of aircraft sold that essentially use this idea, buyers are smaller countries, not the US.
Yep, they put a Rolls-Royce Dart turboprop engine on a modified P-51 airframe. The result was something with a top speed of nearly 500 mph, well with the capability of the P-51’s airframe design given the post-World War II P-51H was capable of 487 mph top speed.