Will a new style Hi Power fit an old style pistol. I am building up one of the Numrich slide/frame sets. Barrel is the hardest part, aside from putting the trigger in the frame. Still haven't figured that one out yet.
Early and late pattern barrels are not interchangeable because the cam lug in the frame is a different size. Even if a barrel is the right type, it needs to be individually fitted to assure accuracy, reliability and longevity. A misfitted barrel will tear up the slide in short order.
I think all of the Inglis guns take the early pattern barrel.