Just like Polos, Golfs and Audi 80s, Audi didn't change much of the chassis during the model changes. What this means is that this 100 (Type 43/C2) shares the chassis with the 100 Type 44/C3 and 100/A6 Type 4A/C4.

I don't know how important it is for you guys to have approval on parts like lowering springs (TÜV is needed here in Norway), but if you don't, you should be able to install lowering springs from a Type 44 without any problems at all.

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If you have a 5 cylinder, you don't need a stereo.

1999 Audi A6 quattro
1990 Volkswagen Golf CL Syncro
1987 Audi Coupe quattro