I’m not sure about the other years, but a 1991 500SL comes with two highs (twitters 1 ½“) up on the dash board, two mid’s (3 ½)on the door panels, and of course two bass (5 ½)on the door panels as well, six total. I’m not positive about the sizes, but the tow on the doors are mounted in a sealed box. The whole system uses 3 olmn speakers. Aftermarket speakers are 4 olmn, you can still use them but it wont sound as good.
I bought my car form an audio sound fanatic. He built a custom stealth box behind the seats that houses 3 JLW12 the whole system uses MB Quart for mid’s and highs with MB Quart crossovers. The control unit is a Alpine CVA 1000, and power is delivered by a McIntosh 4000 amp. Personally I’m looking to put the factory system in it, I like to keep it as original as possible!!!