Motor twisting on mounts and running poorly

[tkarman]

Finally spring and warm weather are here in Seattle so I just uncovered the 72 coronet today to take it out on a quick drive around. It fired up no problem and it purred after warming up a bit. I drove it about 3 miles without problem then I went over some railroad tracks which shook the car up a bit but not terrible. After the tracks the car suddenly started having trouble idling. It died on me at a few lights but I was able to get home. I at first I thought maybe bad fuel from sitting so I filled it up with 92 octane(about 9 gallons). When I got it home I opened up the hood and noticed the engine had twisted toward the passenger side about 5-10 degrees or so. I lifted the front of the car and took a look at the motor mounts. The metal looked intact just the bushing was compressed on the passenger side as well as the transmission mount looking all twisted. I started the car up and put it in reverse which slowly twisted the engine back to center where it stopped. Now I can barely keep the engine running at idle. It will run rough with the RPMs up which makes me think possibly a vacuum leak was created when the engine twisted but I've checked all vacuum hoses I can see.

Questions are:
What the hell is causing the engine to twist?
What should I check on the engine that may be causing it to die at idle.