Replacing the factory under the dash wire harness with an American Auto wire factory wire harness.
https://www.classicparts.com/mobile/1966-Main-Underdash-Harness-w_Gauge/productinfo/52%2D330/
BLAUPUNKT GTHS81 8" Amplified Subwoofer 320-Watts https://www.amazon.com/dp/B08LQ43RGX/ref=cm_sw_r_cp_api_i_6B91DHSVW131KH1SZRAJ
BOSS Audio Systems MC900B 4 Channel Weatherproof Amplifier – Bluetooth, 500 Watts, Bluetooth Multi-Function Remote, Full Range, Class A/B, 4-8 Ohm Stable, Aux-in, RCA Outputs, USB Charging https://www.amazon.com/dp/B00IBI518Y/ref=cm_sw_r_cp_api_i_G5P7VBR4FQX4CMS5T6AQ
https://www.classicparts.com/mobile/1960-66-Kick-Panel-Speaker-Assy-Dlx/productinfo/69%2D874/
https://www.summitracing.com/parts/sum-879006