4 ohm vs 8 ohm

Germanium Transistors were not intended nor designed to be high current devices, 8 ohms was the standard in that time period. The new systems trade high fidelity for higher power using lower output impedances. Your radio is a class A amplifier continuously conducting in that mode. The newer systems are I/C's Class A/B at best most often Class B conducting 70% of the time, causing distortion.