When replacing the engine on a 2001, are there other problems with wiring, etc. on 2001 Lexus ES300

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I was told that when you replace the engine on a 2001 Lexus, you also have to change out all of the wiring...someone is trying to talk me out of buying this car, putting a used engine in it, then re-selling. What do you say?
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I have found that Toyota/Lexus wiring is really good quality, unless it was damaged in some way, say from flood water or rodents ( I am not kidding ) eating it.
Thank you so very much. My boss' wife drove this car...probably 190,000 miles on it. Excellent condition. Then one day, she had the oil changed, and, on the way home, the engine blew. We were thinking they forgot to put the oil in it, but there was oil. Anyway, I want to buy the car for around $600, put an engine in it from a wrecked Lexus, then turn around and sell it for a little profit. But, then some mechanic (that was talking about Lexus' in general but had not looked at the actual car) told me all of the wiring would have to be changed if we put a new engine in it. I'm a woman and don't know the first thing about it. Help....!! Thanks, Fran