White Smoke and Idle ?
 

I just got my 79 300SD running after 9 years of not running. It seems to have a lot of white smoke is this normal? I have never owned one of these before. I also notice it runs really rough at idle and runs good at higher rpm. One other thing I noticed is that the small line from the top of the radiator going to the tank on the fender seems to pulse fluid into the tank is this right?

Blown headgasket. The white is burning coolant and the pulsing is the pressure from the engine's compression/combustion leaking into the cooling system.

Take off the expansion tank cap and listen for puffing or bubbling sounds.

Crud! I have puffing sounds in the tank. How hard is a head gasket to do on the 617 enignes?

I have yet to do it but from everyone description, pretty average. Take it as an excuse to get a valve job and have the head pressure tested as well.

There are really good threads on changing the head gasket on this site in the archives. Plus many other sources. The motavation to do it yourself is the amount that repair shops charge for labour. Much better financially than finding out you have a bad transmission for example.
One caution though if you live in an area that the temperature drops below freezing. There is a good concentration of anti freeze evident?
Car wil be thirty years old in a couple of years so overall this is not that bad if you think about it.