According to the impedance curve posted, these speakers used a 4 ohm woofer and most likely a 6 ohm mid and tweeter. The woofer at one point drops to below 3 ohms, this is most likely why you are reading a 3 ohm dcr. Nominal means no more than average impedance over its operating range.
Also, the method that Erik is referring to, you would add the appropriate resistor to the tweeter only (wherever the caps were replaced)
Also, the method that Erik is referring to, you would add the appropriate resistor to the tweeter only (wherever the caps were replaced)