Some thoughts:

1. Original woofer polyether foam surrounds will have disintegrated into dust a long time ago. If you heard a working pair, you heard woofers with non-original surrounds. It's a roll of the dice as to whether the replacement surrounds perform the same mechano-acoustically as the originals.

2. The Philips midrange surrounds are suspect too. A few decades of passage of time usually does bad, and often unpredictable, things to organic components.

3. Check the condition of the crossover capacitors. Electrolytics "leak" capacitance with time, generally about 1% per year.

The DQ-10 was an inefficient, but great-sounding speaker for its time. Restoring a pair involves many unknowns and may or may not come close to the original. Ironically that may or may not be a bad thing.

For me, I'd buy new.

HTH,
Mark