Hello. Just joined. First post was in vintage section. I am responding to Kyle Pavao's inquirey about 6x9 speakers in rear deck. If you find the speaker mounting depth warrants cutting the steel rear deck of your 123, (which most quality speakers will), be careful! There is steel channeling for the chassis structure (viewable inside the trunk). Also, be aware of the fuel tank and vacuum reservoir that are directly under the rear deck in the trunk. You don't want any surprises.

I recommend purchasing 2-way component speakers for that application. There is minimal customizing involved. Eclipse used to put out ones w/ 5" woofers which would drop right in, but I think those are discontinued. Consider a 5 1/4" size. The tweeter component could be mounted above on the side trim. Cross-over component can mount in trunk.
When I installed stereos in my cars, I make it a point to leave the car as factory as possible so I can reinstall the factory system if I want to. Let me know how you make out.
Thanks.

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GS (tnarg)

'67 200D, 225,000 mi - "FINTAIL", 4 on the floor and loving it!
'83 300D-T, 229,000 mi
'85 300D-T, 234,000 mi
'86 524td BMW, 230,000 mi; In-line 6 cyl. Turbo Diesel !! (BUT I SOLD IT AFTER PUTTING OVER 200k ON)