my 4runner w/ 206K mi replace engine or buy a new car?

V6 engine , since you say it has chain , not belt. To answer your question best , the condition of the rest of the vehicle would have to be known. Do you have a mechanic or shop that you trust with your money?..........and truck? ........IF all else has been well maintained , I would probably go with a good used engine. If it was my own , I wouldn't worry about just head gaskets and chain set , but that's with knowing who's doing the work(me). Personally , mileage, by itself , on most any engine , doesn't mean a whole lot. The type of driving , and maintenance, seems to make the bigger difference , from what I've seen. ............ONE opinion. Good luck