It is likely to be oil leaking through the valves and after sitting for a few hours, there is enough oil that has accumulated to make it smoke during the start. The heads will have to come off to replace the guides. Maybe someone else can give a good answer as to the cost involved.
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record