I have a 1978 dodge truck, 318 2wd. After it has warmed up it starts smoking out the tail pipe, dark blue. Valve seals? Needs an oil change? I don't ever drive it so yesterday was the first time it had probably warmed up in two years, it usually drives from my barn to the field then sits for awhile then back to the barn.
Drive it frequently. If it still smokes, then don't. Sounds like a low effort fix. 
Get it good and hot, drive it HARD for a bit on the highway. See what it does after that.
Its purpose is to supply the motor when I finish the body work on a trailduster I have.
The smoke definitely sounds like oil smoke, but it could be from a variety of causes. Could be bad valve seals, could be sticky rings from sitting, etc. Running it hard will help get the rings moving and cleaned out.
Being that you aren't really driving it anyway, it wouldn't hurt to pull the plugs, put 2 ounces or so of Marvel Mystery Oil (or other similar thin oil) in each cylinder and let it sit for a few days. Turn it over with the plugs out to clear out any extra oil, then put the plugs in and fire it up.
That (especially combined with a hard run afterwards, ideally with plenty of high rpm engine braking in addition to heavy throttle) should do a good job of freeing up the rings. If that doesn't help and it compression tests good, the issue is probably valve seals and possibly valve guides. A bad intake gasket could suck up some oil too.
It won't get a hard run, it is a farm truck and hasn't had a title in the twenty years I've had it. No road drives for it
Ah. Definitely do the MMO thing and compression test it then. That's about the best chance you've got at narrowing down the problem to major or non-major without really being able to drive it.
Once the corn is off I can lol
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