Francis:
I just changed all 4 of my speakers in my 89 300E, and it was a pain in the butt. You will not have a large variety of speakers to choose from. The front carry 4"s, and the rear deck holds 5"....I put 5 1/4 in the back, they are alittle bigger, and you will have to make some modifications. I think Polk carries the rear deck speakes, which are about $89 from Crutchfield. If you want beautiful clear sound, go with JBL's like I did

Agron
1989 300E