I don't know how the '79 SD dealt with blowby gasses. I would route the blowby from the valve cover to the plastic u-tube that connects the air filter housing to the turbo. That would probably be the easiest thing to do. FWIW, that's how its done in my current car.

__________________
2001 Dodge Ram 2500 Cummins Turbo Diesel - 4x4, auto, 3.54 gears, long bed
-------------------------------------
'92 300D 2.5 Turbodiesel - sold
'83 300D Turbodiesel - 4 speed manual/2.88 diff - sold
'87 300D Turbodiesel - sold
'82 300D Turbodiesel - sold