When I first got the C280, it had the cassette holders too. But the 96 and later C-classes had the storage pocket there. I went to the dealer, bought the pocket ($11), and it fit perfectly, but that's because it was the same model and all. That is too bad the 190s never had a little pocket. My storage bin where the cupholders are now was able to retrofit the new cupholders of the 96 and newer C-classes also. It was all too easy!
I'm sorry to hear it was a little harder for you, but I would really like to see the pix when you are done with it!
2006 E350 w/ 155k miles (Daily Driver)
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)