Are all Mercedes heads the interference type?

If there are some that are not, is there a reference list somewhere as to which are and which are not?

If they are all interference heads, or for those that are, how often should the timing chain and guides be changed to prevent that pesky bent valve situation?

The models I currently have are 190E 2.6 (two of these) both with about 190k, 300SEL with about 190k, and a 420SEL with 130k and a dead engine (due to failure of a timing chain guide rail).

Thanks.
-Brett