Chris, a search of the site under terms like speaker, upgrade, head unit, etc. will turn up more than you could possibly want to know, especially on speakers. Of the head units out there, I found Blaupunkt made more over the years that were cosmetically compatible than anyone else; I put a Honolulu in mine (bought on Ebay) that turned out well, but there are some other models that match really well with the appearance, and most are at least acceptable (i.e., will comfortably outdo the Becker that was OEM). Obviously, I was interested in appearance first, but I did want decent sound; it just seemed logical to realize that an open car doesn't do justice to an extravagant system. I found Ebay a continuing source of ideas, and Blaupunkt's own site as well as Continental and one other I forget are also sources of info on models over the last several years.
A few Blaupunkts that seem cosmetically OK to my eye, and use amber or yellow displays to go with the dash lighting
AFAIK; I'll post because I never found such a list compiled before, and there are probably others I'm missing.
ACD2800
ACD2900
Aspen CD42
Miami CD42
Florida RD168
Nevada RDM168
Madison CD127
Honolulu CD50
They'll vary significantly in vintage, power, features, etc.--my Honolulu is a good but not great cosmetic and style match, but works very well. All are no longer current, but can be had used, occasionally in essentially NIB condition.