Thanks Klaus for your reply.

I got the car home, but decided to pay for a tow instead of risking entirely ruining the head/engine.

Didn't have time for too much troubleshooting, but did confirm major coolant spill inside the cabin. I did add a quart of oil, but the oil now looks too full, so perhaps it has coolant in it...plan on draining/re-filling the oil and by passing the heater core to isolate the coolant leak and seeing if I can find the oil leak.

I was also going to pressure test the engine - will that enable me to determine if there is a head gasket failure? Or should I invest in a cooling system pressure testing tool?

The bang also bothers me as well. I don't think it was an A/C issue; would the head gasket blow with enough pressure to make a loud bang? I think it was on the coolant side, as the cabin filled with coolant gases right after the noise. I didn't hear and major bearing noises.
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