Radio/Speaker Questions

’72 Demon - original radio, what ohm speaker was radio designed for ??
I have a 4 ohm speaker in dash and two ( 4/8 ohm compatible) speakers under rear package tray with a factory fader switch. No speakers are original. What should the wiring diagram look like for this configuration ?? The radio (am only) seems to work fairly well but was thinking I might get better sound by changing wiring pattern (in case it is off somewhat).
Trying to understand the information I have found seems to confuse me even more.
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