That is too high a price. There are plenty of IFS 4-runners out there with no engine problems. As for anything to look out for, come awn its a toyota! As long as you change the oil regularly and do the timming chain every 150,000 or so they can go for about 500,000 km.
I bought my 88 Runner with a milkshaked engine for 950 - came with: New back window/motor, Rebuilt rear driveshaft, Optima battery less than 1 year old, Minimal rust. Why pay $6500 for one that needs engine work. My opinion is a $6500 87 Runner is a perfect, low mileage stock one, Or one with well done modifications which would cost you more to do yourself than you are paying for the truck.