head casket on 2003 Lincoln Navigator

We were driving to Arkansas from Dallas this past Sunday. After a brief stop to get a drink (left engine running) we were pulling out and there was this loud noise like maybe a belt had broken and was hitting something. We couldn't find anything. No oil leaks, etc. We continued and the catalytic converter light kept flashing on and then going off. We lost some power, but the motor only sounded bad when slowing down, or extreme pull like on hills. We watched for overheating, oil leaks, etc. but nothing. We were able to get the car home. We were told by the Lincoln dealer that it was a head and the cost would be around $5,000. What is your opinion about repair and price.

Asked by for the 2003 Lincoln Navigator
Did the shop say what was wrong with the head? Are they recommending replacing 1 head or both?
In contacting the dealership, I have found the following information. I need the drivers side cylinder head, replace ignition coils #7 and #4 and replace the spark plugs.
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hope you didn't spend $5000