[68c10airstream]

72KOOL, as a past dealer mechanic living up north in the cold and did a lot of drivability work and you live in nebraska with a daily driver i believe vortec heads do not have a exhaust heat crossover so you end up with a cold intake manifold. Your mileage and drivability will be poor, more unburned fuel in the oil, etc, etc.

If the existing engine does work well in warmer months and is a little "off" in the colder months address this along with fixing oil leaks starting at the top and work down.

For the best 70's cold weather drivability and mileage these parts are a must;

Heat stove on i believe the pass. side exhaust manifold.

Heat stove pipe connecting the tin stove to the proper stock air cleaner.

Double check the intake manifold getting real warm to the touch right where the intake connects to the heads in the center area where the exhaust crosses over from side to side during a cold startup. If not remove intake and proceed to chisel out the hard carbon in the heads/intake. This heat cross over is called E.F.E. which stands for" early fuel evaporative" It is designed to warm up the base (or floor) of the intake where the incoming fuel/air mixture goes through the carb and turns 90 degrees at the floor to branch out to the cylinders.

The last piece (it's usually the hardest part to convince is needed) is the heat riser on the rh manifold where the "Y" pipe hooks up. It gets a bad rap for rattles and sticking but it was the 70's. Without the heat riser it just takes longer for the intake floor to warm up, especially if the truck has true duals.

Your oil smoke on start up is probably valve stem seals. When all of the above systems are working correctly, that oily first start up coats the crossover and will cause hard carbon in a matter of 2-3 years of driving. In the 80's fixed many mopar 318 v8's for carboned plugged crossovers. Oil dilution, this gassy oil eat up plastic covered cam sprockets, shed the plastic into the pan and plugged the oil pickup screen and lifters would complain. If i haven't bored you by now i at least got you to think of what happens and you are better informed than before. My mission is done and enough of my rant. I'm here if you need me and good luck.