Hi! I am a newbie to this site, and I decide to post because this morning the timing belt on my '83 240T broke, and I had it towed to my mechanic. I used to sell parts for these, and while I could probably tell you the part# for the belt, I am not sure if this is an interference engine.

The mechanic says it is, while some other guy on another forum says it's only interference engine if the head has been shaved or the block stacked. I am pretty sure this is the stock motor (B21FT?) - but I am waiting for the bad news right now and was hoping someone could assuage my deepest fears about bending a bunch of valves.

I was driving it about 50mph when it broke - no big banging or cliking sounds...

It shouldn't be an interference motor.
You'd have to have some very aggressive/non stock cam profiles to get it to bend valves and/or like you said a worked over head.