The old speakers I've heard are not remotely flat. But they do sound big, and fun, and maybe you can just EQ out the speakers with a modern receiver's room correction.
The sound beautiful, at least to my old and abused ears, for both music and movies. (I use them as stern + a su=ingle sub for music, and as part of a 5.1 system with a centre speaker and rears for movies).
They aren't quite 70's old. But they were a long way from new when I got em off eBay a decade or more back.
I also still have the first speakers and amps I ever bought, back in 1988. Boston Acoustics A60MkIIs and a NAD 1100/2200 opre/power amp pair. This speakers have has 3 or 4 new drivers (all due to party abuse) and the caps in the crossovers replaced every decade or so, and the amps have had all the electrolytics replaced a couple for times. They still provide great sound in my dining room.
(And I've become a bit af a NAD/Boston Acoustics brand-tragic. I end up drunk eBaying both brands every now and then, I have a pair of A40 speakers on my desk here, The lounge room home theatre amp is a NAD 70W per channel amp. And I've got most of a setup of a pair of A40s, a NAD 3020, and an Apple Airport Express together as a birthday present for a friend in a few weeks...)
I met a guy who had a pair about 10 years later. I offered him double what he had paid for them new. He wouldn't let them go, either.
Combined with this software: https://www.roomeqwizard.com
It kicks ass!
If you compare 128 kbps MP3 files to a CD the difference is night and day. 320 kbps MP3 is transparent, 192 kbps is not bad for most recordings. As I am writing this I am working on a python script that recompresses FLAC files from my music server to put on a USB stick for the car or for my Garmin watch. Right now the target is 192 kbps AAC for the car and the high end of the spectral band replication range (maybe 64-96 kbps) for the watch.