[Lord Accord]

Its hard to say.
I would start with a compression test.
It sounds to me like whoever worked your head didnt put new valve seals in, and theyre leaking. I would think that if it was the rings it would smoke more than a few minutes after you crank your car up, but I dont know.

Are you positive it doesnt smoke all the time, especially when you take off or speed up(give it throttle in any way)?
I had a problem like that in my truck that I didnt notice for a while because the smoke was so light. It smoked when I first cranked it up, but thought it went away, until one day it got worse and I finally noticed it was smoking all the time.
By the way that problem ended up being a cracked head.

 

[Lord Accord]

A compression test wont DEFINATELY give you the answer, but it will give you a real good indication of what it PROBABLY is.
It sounds to me like bad valve seals. If it were your valves it would smoke more than a few minutes, and I doubt it would run all that great.
There are different ways to do the test to see if its your rings or valves, so make sure you figure out how to do it right, from there you should be able to figure out what your problem is.