I enjoy originality also. And although I’ve seen there are a few individuals that offer to add Bluetooth, the cost is pretty hefty especially if you’re doing such a thing on the 70-77 radios. I think I have a post here still otherwise it was pre crash and is gone but what I did is I installed a small Bluetooth enabled amp under my center console. I installed a factory 70-77 red dot stereo and my console mounted 8 track player. As most know those use common ground speakers and require 8-10 ohm speakers. And only two at that. With the amp, both original devices function as they did but feed into the amp. I split the signal from each speaker going into the amp and the amp outputs two left and two right channels so I can power 2 modern 4 ohm rear 6x9s and a 4 ohm “dual coil” front speaker with left and right input/output.
It’s not a perfect setup as far as sound quality since I’m limited by the radio and 8 track outputs but suits my needs and the Bluetooth output can be adjusted by an EQ on my phone. There’s a wired remote I hid in the ashtray that is used to turn Bluetooth on and subsequently change Bluetooth volumn, tracks play and pause.