Hello A. Bruinenberg
Of course it is possible to replace the original speaker by those from new production. I do not believe that it is important what kind of magnet the new speaker has. He must also have the same mounting dimensions (8 inches), the same frequency range (mid-range), the same impedance (8 ohms) and about the same power consumption (about 5 watts). Whether the sound is good, you can only find by trial. The success depends on many other factors, such as resonance frequency, sound pressure, frequency response, efficiency and the like.
The HF100R is one of the greatest sounding Jukes. The individual components are perfectly matched. A speaker must not only match the other speakers, but also to the cabinet, to the amplifier and pickup. This is especially true for this model, because there is no crossover (apart from a capacitor for the tweeter). The division of the frequency bands is done only by the characteristics of the speakers. For that reason I avoid to install new speakers, but let recone the original speaker if possible. You can get a good sound with new speakers, but he will always be different than the original speakers.
Best regards - charly49
