I just purchased a 1984 300D Turbo yesterday. The car has 226k miles on it.
After I bought it I drove it around 50 miles to my father-in-laws house since we were so close. On my trip home I've noticed that it is now backfiring.

I drove it nearly 170 miles before it started. At first it was an intermitant pop, but eventually it would turn into a constant rumble. As I slow down the backfiring stops and it humms quietly at idle. After about 10 minutes back at speed (70 mph) it starts to rumble again. Oddly enough it appears that when the backfiring started the engine started running cooler. I didn't notice any loss of power while it was backfiring.

Perhaps 50 miles before this started the muffler bands snapped and I drug the muffler for maybe 2 miles before I got it tied back up.

Could the muffler falling have damaged it to the point that 3,500 RPM is too much pressure for it?