So in total the truck has 300k miles, and at 168k the motor and tranny were rebuilt, or the motor and tranny has 168k since they were rebuilt? To me thats alot of miles though there was a truck here that had 500k on it and was a 97. My 94 chevy has a total of 225 rebuilt motor 25k miles back and just got done rebuilding tranny again. If the truck was taken care of, and maintained like it should have been then it should be good, though the one thing I would worry about is the tranny, pending how it was rebuilt, with that many miles on it, they tend to blow the 3-4 clutch pack, ask me how I know. Other than that these year of trucks are tough mine has been though hell, it had 135 k when I bought it 8 years ago and now has total 225K and runs like a top.
To me body mileage is nothing, its the motor and driveline, ball joints, tie rods, rearend, wheel bearings and axle the things that get the most stress and wear look it over real good. Look for signs of leaks, or smoking. If it smokes any its likely its wearing out.