Highest Amp Alternator For a 72 Duster

high amp draw should bypass the ammeter and bulkhead connector. 4 channel head unit with electronic crossover, point low frequency toward huge bass amp, bridge it and run both subs in series, careful not to exceed ohm rating of amp (2 8 ohm speakers in series makes a 4 ohm) Bass is not directional and is usually not seperated spatially channel wise.
run the 4 channels into a 4ch amp to maintain fader control. a member here does this for a living, he will probably chime in and tell me how wrong I am :-)

alt output is what your system will draw. watts divided by voltage = amps. so a true 1000w amp will draw up to 83A (class dependent) and you'll need a 4G wire to run it off the battery.