328 Sound System Upgrade

I did this some years ago & also installed a Subwoofer in the passenger footwell (since removed). The amp for that went on a board that sat inside the spare wheel (also now removed). I made a pair of speaker pods for the rear parcel shelf as well which help a bit because of the proximity to where your ears are (!)

Upgrading the door speakers and the tweeters is not that difficult though the doors do need quite a lot of work to seal up the apertures and add sound deadening. The backing for the door cards is fibreglass & the speakers are behind that. The holes in the fibreglass (behind the carpet) are not even big enough for the factory speakers so they need opening out. Its easy to do and isn't visible once the cards are back in place. ISTR you need 6 1/2 drivers but they need to be fairly shallow so as not to interfere with the window. Mine are Alpines.

For a period correct head unit maybe look at some of the Blaupunkt stuff.

I used an Alpine head unit and added one of their power pack mini amplifiers which is hidden under the centre console in order to boost the output. I might well move that to the passenger footwel behind the plate where there is a small void now that I removed the Sub.

Otherwise its a difficult car to put audio gear in because there is very, very little room - and then its noisy on a good day, so overall the results may not justify the effort!

 

For your head unit, the re-issue Blaupunkt Bremen is a great choice. I believe the original came out in '86 so it'll be period correct, and the re-issue version has bluetooth, and it has USB and card slots under the door where the cassette used to go.

Bremen SQR 46 DAB - Blaupunkt

 

Blaupunkt and pioneer have new 'retro' head units that look period correct but don't take physical media so that was a deal killer for me.
Edit: apparently the pioneer retro unit isn't coming until Q4 25