White Smoke Troubleshooting

Hey guys, looking to buy at an early 99 F-250 (191k)that the owner claims puffs white smoke and runs a little rough for about half an hour until warms up. Owner also claims that truck will idle all day long, and white smoke and rough running doesnt come back until next morning when you start the truck. I am in NC, and this thing is in FL, so I would hate to go all the way down there to have it be something major. Is this a textbook injector problem??? I have been told that its injectors... am I on the right path??? With the miles on the truck, would you guys replace all the injectors, or just bad ones?? I dont have the time nor facility to do it myself, so what am I looking at shop wise to replace what is needed (per injector, etc?) Thanks for the help!!!

Nick