Unlikely you damaged the engine. Cast-iron heads don't warp like the aluminum heads on later engines (1986+ 300D's). Look it over in the morning. Most likely, the relief valve on the expansion tank just released (~16 psi?).

Yes, the alternator in my 1985 300D seized (jammed bearing) soon after I got it and burned up the belt(s). Actually might have been just 1 belt on when I bought it (didn't know these engines then). I left the car on the side of the road since a co-worker stopped. I returned after work and tied a nylon rope tightly (barrel knot) so it turned the water pump/fan and drove 2 miles home. Another time, a large metal plate popped up on the freeway and cut off both alternator belts. I came back after a 3 hr class and drove home 10 mi, watching the gage. It got to ~105 C, so probably OK. Ambient was ~50 F.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans