Hi I am looking to redo the sound system on my 1986 190E 2.3-16. The stock speakers front and rear are 4" each. What is the largest speaker I can put in the stock locations especially in the front and how do I do that? I know the later models have 5.25" in back so can I put that or even 6x9" in back? Also, how do I add two subwoofers in the doors like the later 1992+ 190E with active bass? Do I need the door panels and what else? Thanks very much.