Well I was going to wait to post anything about this until I tried it and could attest to whether or not it works the way I plan BUT in order to keep Roger from pulling the plug, here goes.

After 8 years of owning my car I finally installed some speakers and a modern single DIN radio in my map pocket since my radio opening is uncut. Some previous owner of my car bent the area around the package tray speaker holes to drop 6x9s in rather than mount from below. Not sure if I should have tried to bend it all back straight-ish but in order to fit my new speakers I had to bend a slight bit more....
Anyway, my current setup isnt anything fancy but sounds as good or better than my 2010 Ram which has a decent stereo. I did the dual coil front speaker and the two 6x9s i mentioned already. All are modern 4 ohm speakers. My only gripes are I don't care for the look of the modern radio in the map pocket and that particular radio I have (though it sounds great) lacks bluetooth which leads me to my plan.
I had a 70-77 delco radio I bought a few years ago in rough looking shape for pretty cheap but it was DOA when I tested it this year. I took it to a local vintage audo shop and though they were able to clean it up and replace the lens there was apparently a fried chip on the original amp that couldn't be sourced nor replicated apparently. Their solution was to add a modern amp which would now power a left and right channel via positive and negative wires for each channel contrary to the common ground used all fine and dandy except I’ve always wanted an 8 track player added into the mix which now probably won’t work with the converted stock radio and 4 ohm speakers.
Part 1 of my plan is to head back to said audio shop with my recently purchased 8 track player to see if they can maintain the same functionality of the 8 track but install a modern amp into it like they did with the radio. That way in theory I should be able to connect the factory radio to the 8 track track player which in turn connects to the speakers in relatively the same way it did in it’s factory set up. With no tape in the radio should get power and send the speaker signal through the 8 track to the speakers and went to tape is inserted the tape player should cut power to the radio and play the tunes through the modern amp into the modern 4ohm speakers.
Part 2 of my plan is this amplifier.
https://www.walmart.com/ip/Kenwood-KAC-M1824BT-Compact-400-Watt-Bluetooth-Connected-4-Channel-Amp/44641023?wmlspartner=wlpa&selectedSellerId=5700&adid=22222222228032076958&wl0=&wl1=g&wl2=m&wl3=61126786856&wl4=aud-566049426705:pla-108530188136&wl5=9015090&wl6=&wl7=&wl8=&wl9=pla&wl10=117878170&wl11=online&wl12=44641023&wl13=&veh=sem&gclid=EAIaIQobChMIhYiCr6_L3wIVhjxpCh3X1weoEAQYAyABEgItXPD_BwEIn case the link expires it’s a kenwood KAC-M-1842BT. It is 400 watts which should be plenty for me, small enough to mount in several places, has speaker or line level inputs which should make hooking it up to my factory radio and eight track player, which will have speaker level outputs, easier and the icing on the cake is that it has a Bluetooth radio built-in with a separate controller. You can either control your music directly from your phone or using the controller which I plan to run through or out from under the center console so it is not noticeable. I am also going to use a splitter to split the left and right channel so that there will be two left and to right channels from the 8 track/radio combo so I can power all four channels of my current speaker set up. I will still have the factory balance control with the eight track player and the radio and the amp has fader control built-in for the Bluetooth function only.
The last thing I will really be lacking is an equalizer to adjust sound quality. I will still have the tone control from the 8 track player and the factory radio but that will probably be the extent of how I can manipulate the audio. For music I play on my phone, which is probably honestly what I will do more often than not, there are a few apps that I have played with that function as a graphic equalizer so I should be able to fine-tune the sound of my Bluetooth audio. But I will also be able to pop a tape in or turn on the radio and at least have decent audio from it.
Sorry this turned out way longer than expected. LIKE IT? DONT LIKE IT? Any comments or feedback is welcome and appreciated. I’m no audio guru so if you foresee problems with my plan please let me know. I just thought some others may like to see in case some of what I do benefits them. Ultimately to the overall cost of installing this is going to be relatively small. And yes I know I could mount my current single DIN radio in the glove box but honestly I’m not crazy about that idea and still lack the Bluetooth function.